The Infamous Stringdusters were gathered at Nashville’s Sound Emporium Studios, counting down the intro to backwoods bluegrass scorcher “Run to Heaven,” when they received an urgent phone call. It was Crooked Still singer Aoife O’Donovan, whom the band had requested to sing on the finished track, an eventual standout on their sixth LP, Ladies & Gentlemen. The Dusters were hoping the song’s key was appropriate for her range—but since she’d been overseas and hadn’t given the final word, they planed to roll the dice and record blindly. “We said, ‘We’d better take that call,’” guitarist Andy Falco oŸffers with a laugh a few months after the album’s release. “She gave us the key. And it was a diffŸerent key, so thank God.”

It’s a miracle that Ladies & Gentlemen, an eclectic collection in collaboration with a crew of female vocalists, even exists one year after that well-timed phone call. The process, which Falco calls a “logistical puzzle,” was filled with nonstop coordination, a few false starts and several moments of wondering, “Are we really going to pull this offŸ?” After five days of recording the basic tracks in Nashville last summer, the true work began—assembling their dream team of frontwomen.

The dizzying lineup unites bluesy folk-rockers (Joan Osborne), R&B belters (Joss Stone), singer-songwriter legends (Mary Chapin Carpenter), country hitmakers (Lee Ann Womack) and prog-grass all-stars (Sarah Jarosz and Sara Watkins). And all of these musicians— some longtime friends, some strangers—were eager to accept the challenge of becoming honorary Dusters. During the band’s first decade, the all-male quintet—Falco, bassist Travis Book, fiddle player Jeremy Garrett, dobroist Andy Hall and banjoist Chris Pandolfi—has developed into a startlingly versatile unit live in the studio: Like their fellow string-band virtuosos, the Dusters have rattled the foundations of bluegrass by weaving Americana, rock and jamband influences into a style that’s difficult to categorize. With Ladies & Gentlemen, they tailored songs to specific vocalists—a unique strategy that expanded their sound even further.

The female collaboration concept had been kicking around Camp Duster since Falco joined the band in 2007, replacing original guitarist Chris Eldridge, who fled to join Chris Thile’s Punch Brothers.

“The first thing I can remember is the first session I did as a Stringduster—we did a demo session for an incredible singer-songwriter named Sarah Siskind [Book’s wife]. We did it live, and they were her songs. We had such great fun doing that session. I don’t think any of that music has been released, but it was an early thought that this would be a cool thing to do. Flash-forward several years: Joss Stone, who is a friend of mine, came to one of our shows in New York and jumped onstage to sing a tune with us. We thought it would be cool to do a track with her. Then we thought it would be cool to do an album. Then we thought it would be great to have several guests.”

By 2015, the Dusters had earned enough clout in the music industry to make that dream a reality. They’d become staples of the jam and bluegrass circuits, with enough mainstream appeal to earn a Grammy nod in 2011. They’d even founded their own three-day music gathering, The Festy Experience, based near their one-time home of Charlottesville, Va. Using their own connections—and the skillful persuasion of their management team—the band plunged forward with the idea, recruiting the perfect voices to match each of their tunes.

“It’s a massive undertaking to put together all these guests with everybody’s schedules,” Falco says. “There were some folks we reached out to who were maybe making their own record or were on tour and weren’t able to make it work. But when you go into a record like this, you have many more songs than you expect to release and you reach out to X amount of singers, hoping that a certain percentage of the people you asked would be able available to make a complete album. Then you place a lot of songs to the singers that were able to do it.

“There were a few singers on there that we’d never met but asked to do it,” Falco continues. “It’s probably one of those ‘Our people called their people and they did lunch’ kind of things. But they were people we really admired, so we reached out that way. Joan Osborne, for example, none of us had ever met. But we all loved her work, so she came up as someone we thought would be really cool to ask. Most of them, though, we called ourselves, friend-to-friend.”

Falco credits producer Chris Goldsmith, who coordinated the complicated logistics of recording the songs, as the album’s MVP. Without the luxury of having all the singers in one studio, Goldsmith closely monitored the women’s touring schedules, often arranging to meet and record near his home in California. Several vocals were recorded independently and emailed over. Goldsmith even flew to New York and hunkered down there for one session.

That grueling process paid o•ff. With its clean contours and wide textural scope, Ladies and Gentlemen marks another chapter in the band’s evolution away from traditional bluegrass sounds— one that began with their third LP, 2010’s Things That Fly. That album—highlighted by a string-band remake of U2’s anthemic “In God’s Country” and their spunky, Grammy-nominated instrumental “Magic #9”—incorporated new instrumentation (organ, viola) and more polished production elements.

And The Infamous Stringdusters have continued to experiment and take risks. For 2012’s Silver Sky, they worked with producer Billy Hume, best known for his work with rappers like Nas and Ludacris. They’ve also showcased their range with cover tunes during their highly improvisational shows, tackling everything from the Grateful Dead’s “Scarlet Begonias” to Lorde’s ubiquitous electro-pop hit “Royals.” (They recorded studio versions of some fan favorites for last year’s wide-ranging Undercover EP.)

Another major shift came in 2011, with the departure of founding mandolinist Jesse Cobb. While the band originally intended to find a replacement, they realized they “really clicked” as a quintet, utilizing more space to declutter their songs.

“There is a slight rhythmic shift, a little bit of an adjustment in the way you approach the rhythm,” Falco admits. “We were able to fill that void with what we already had. It felt right to us, and it opened up a lot of space. In a band like ours, there are a lot of soloists. It’s no slight against Jesse, but having one fewer soloists isn’t a bad thing in our band.”

Compare the Dusters’ 2007 debut, Fork in the Road, to Ladies & Gentlemen, and the shift is startling. These are the most disciplined and accessible songs in the band’s catalog, with the female voices unearthing soul and charisma— from the jazzy “Have a Little Faith” (featuring Stone’s bombastic croon) to the hooky “Won’t Be Long” (guided by Sarah Jarosz’s deft vocal leaps).

“The ladies all really put their own touches on the songs, and that wasn’t micromanaged by us,” Falco says. “We sent them the tracks with us singing them, just to give them an idea of the melody, and it sounded weird because it wasn’t keyed for us. They all took that and brought it to the next level by putting their own spin and touches on it. It made it feel more like a collaboration. Every time we would get a track back, we didn’t know exactly what to expect.

“Over the years, there have been so many dudes in our band, so it’s nice to bring a little more of that [female] perspective to the songs,” he adds. “It was a challenge, too, writing songs for this album— trying to be sensitive and take on a diff•erent point of view.”

The Dusters faced another challenge in figuring out how to tour behind the album. Would they bring out di•fferent singers at di•fferent shows? Handle the vocals themselves? The solution ended up being obvious: hit the road with their unofficial sixth member, Nicki Bluhm. The Gramblers singer-songwriter, who adds a gentle twang to “Still the One” on the album, has been in the band’s orbit for several years, having joined the Dusters a while ago for a winter ski tour.

“It was gnarly,” she says of the trek. “We went out without our drummer because we thought they wanted a more mellow, string-band type thing. We were in my little Ford E-150 white cargo van and had to add a jump seat to it. And when you go on those tours and face the weather, you really bond. The two bands really just hit it o•ff, and we all fell in love with each other. We’ve developed a relationship over the years by seeing each other at shows and festivals, and have become brothers and sisters. They had us play their festival, and we just kept doing stu•ff together.”

Bluhm says that singing “Still the One” and touring with the Dusters was “in the stars”—an extension of the good vibes they’d accrued years earlier on the road. “When they approached me to sing a song on their album, I was totally honored. It’s ironic because the song is so opposite of what was going on with me in my life at that time,” admits Bluhm, who recently split from her husband and creative partner Tim. “But the cool thing about performing other people’s songs is that you get to escape your own life for a little while and be in somebody else’s.

“I knew that I was going to like whatever they sent me,” she continues. “They were really cool, like, ‘You can do whatever you want with it—change it up, whatever you want to.’ I loved the simplicity and sweetness of it, and I didn’t really change anything. I just sang it the way Travis did on the demo. It was a pretty quick turnaround—I probably listened to the song 10 times or something, then wrote out the lyrics, tried to get my head around it. I was thinking about Travis and his wife when I sang it—they have such a cool relationship.”

Working with Bluhm also opened up another door for the Dusters: collaborating with indie-folk hero Ryan Adams. The singer-songwriter became a Bluhm fan via The Gramblers’ popular YouTube series the “Van Sessions,” in which the band covers classic pop/rock tracks (everything from the Grateful Dead to Hall & Oates) while hauling down the road on tour.

“[Adams] was one of the people who participated in the tweeting frenzy,” Bluhm says. “That was such a cool experience. Everyone from Cameron Crowe to Bette Midler to John Oates to Ryan Adams—the range of people those Van Sessions aŸffected was pretty remarkable. That’s how he discovered me and The Gramblers. I first knew of Ryan because I was really into Waiting for Guffman and Best in Show, all those Christopher Guest movies, and I adore Parker Posey. I was looking her up years ago, and that’s how I stumbled upon Ryan’s music. [Ed. Note: Posey and Adams were a high-profile couple for several years.] A friend of mine gave me [Adams’ 2007 LP] Easy Tiger, and I fell in love with it.

“We were in each other’s social orbs, and we were keeping track of each other’s careers peripherally,” she continues. “It just sort of happened. We were put in touch, and we started talking about music. He had some shows that he was supposed to play solo and said, ‘Do you know a bluegrass band?’ He knew I was out with the Dusters—we’d become friends. He was like, ‘Do you think the Dusters and you would be down to back me?’”

In June, the seven-piece supergroup united at Colorado’s Telluride Bluegrass Festival—after squeezing in only two rehearsals, one of which took place the day of the show—performing both Adams material and left-field covers, including a haunting version of Dio’s metal anthem “Holy Diver.” (“He just threw that on us at rehearsal—nobody knew that until the day before,” Bluhm admits. “I went and looked up the Dio version and was like, ‘Oh, my God, that’s so crazy. The fact that he can have an ear for a song like that and make it completely his own, that’s so rad.”) The chemistry was so immediate that Adams asked the band to join him at his next few solo engagements, including a set at the Newport Folk Festival, one headlining date and a spot on The Late Show. Stretching perceived notions of what bluegrass instruments are capable of, their stop at Port Chester, N.Y.’s Capitol Theatre included Slayer and Black Sabbath covers.

“We are all fans of Ryan, so it’s very exciting to play that music,” Falco adds, seemingly amazed at the snowballing speed of their collaboration. “It’s incredible to play with a once-in-a-generation type of artist. Just being able to be around somebody with such talent—hopefully it’ll rub offŸ a little bit.”

The humility of that last comment is telling. Ten years deep, the Dusters have broadened both the mass appeal and sophistication of their music, soaking in influence from unexpected sources. Falco and company are willing to share the stage or studio with anyone—an indie hero, a country legend, an emerging soul singer—who might help them develop as musicians.

“We’re constantly trying to evolve,” he says, “being open, allowing the music and the band to take a life of its own.”