Fans who come to see the Avett Brothers expecting the stripped down, acoustic performance that was the folk-rock group's trademark for its first decade are in for a whole new experience.

Brothers Scott and Seth Avett and Bob Crawford now have plenty of company on stage — drummer Mike Marsh, keyboardist Paul Delfigia, cellist Joe Kwon and fiddle player Tania Elizabeth. Crawford likes what he's hearing and seeing.

"What we found when we hit the stage a few nights in a row [recently] was that we are kind of sitting on top of a powder keg as far as sound," Crawford says in a phone interview. "And we can take these songs that were originally recorded with three instruments and work them to seven, really expand them, create a lot of depth, a lot of new harmonies.

"We've got a lot of capability that we are really working hard to unleash," he says. "It's a gradual process. But again, not to beat a dead horse, but 2014 is going to be full of those kinds of moments of discovery."

The Avett Brothers also is expanding its horizons with the song selections in its shows. In its first shows of 2014 — a three-night stand in St. Louis that Crawford referenced — the group played almost entirely different songs each night. That trend will continue, Crawford says.

"We did about 70 different songs in three nights," he says. "So I think we're finally beginning to realize that potential that I would put in the vein of the Grateful Dead, where you've got this mass of material that you're sitting on top of, and it's only right to kind of go through it and do as much of it as you can."

The beefed-up lineup and live sound shouldn't come as a total surprise.

Formed in 2000 by brothers Scott (vocals, banjo, harmonica, guitar, piano) and Seth (vocals, guitars, piano), the group evolved into a trio in 2002 when bassist/fiddle player Crawford joined. That year, the group released its first full-length studio album, "Country Was." A concert CD, "Live at the Double Door Inn," followed later that year.

Over the next four years, the Avett Brothers steadily gained attention in the alt-country/Americana scene, as the group released such well-received albums as "A Carolina Jubilee" (2003), "Mignonette" (2004), "Four Thieves Gone: The Robbinsville Sessions" (2006) and "Emotionalism" (2007).

The albums all highlighted strong songwriting, but mainly stuck to a rough-hewn, largely acoustic sound.

That sound changed dramatically after the Avett Brothers signed with producer Rick Rubin's American Recordings label and partnered with Rubin for the 2009 album "I and Love and You."

That CD retained the Avetts' acoustic foundation, particularly on songs like the folky "January Wedding" and "Ten Thousand Voices," but broadened its instrumental and stylistic reach to the point that the group could no longer be placed in specific musical categories.

For example, "Head Full Of Doubt/Road Full Of Promise" was an expansive mid-tempo track that used piano, drums, strings, organ and electric guitar to help create its beauty. "Kick Drum Heart" was a concise and catchy pop-rocker. "Perfect Square" covers considerable ground, opening as a lovely ballad before kicking into more of a poppy piano-centric rocker. The title track, meanwhile, was a strikingly elegant, piano-based ballad.

The group continued down a similar path with its next two albums — 2012's "The Carpenter," and its current release, "Magpie and the Dandelion" — both of which were also produced by Rubin, who eclectic resume includes albums by Beastie Boys, Slayer and Johnny Cash.

On "Magpie," for instance, "Open Ended Life," with its gracious vocal melody and prominent use of fiddle, banjo and harmonica, could have worked in an austere instrumental setting. Instead, the group gives the song a tasteful jolt of energy with a frisky beat and a little electric guitar.

"Another Is Waiting" is a similar case, as the group muscles up things with an assertive beat, full instrumentation and vocal harmonies. "Vanity" starts out on an elegant note before exploding into an epic rocker. Even songs that remain stripped back, such as "Never Been Alive" and Bring Your Love To Me," get supplemented with drums and other judiciously applied instrumentation.

The songs on "Magpie" come from the same recording session that produced "The Carpenter." The group had amassed a backlog of songs by then and recorded some 30 songs during the session.

"We had a bunch of songs that were moving toward being considered for recording. We just said 'Why don't we just record them all?'" Crawford says.

Once the songs for "The Carpenter" were selected, the group left the studio with no set plans for the remaining songs. In the summer of 2013, at Rubin's suggestion, the group started entertaining the notion that its next album was essentially already recorded.

"I think it was really Rick's idea," Crawford says. "Rick began to sequence them and Rick said 'We've got an album here. We've got something that's fresh here and kind of stands on its own.'"