Watching Brittany Howard perform onstage with Alabama Shakes, it can be hard to imagine her as ever being anything less than a star. A powder-keg of emotion who dominates both her guitar and the microphone, Howard obliterates fashion-magazine notions of what’s important about rock ’n’ roll when she steps forward and lets loose.

But it’s not like Alabama Shakes was somehow destined for the big time. Though the group’s second album, "Sound & Color," topped the charts upon its April release, guitarist Heath Fogg reminds that the view was quite different from where they were just a few years ago.

"It was tough early on," Fogg says. "Even though Brittany is so captivating now and people love her so much, we used to play sports bars in Huntsville, Alabama, and we couldn’t pull a crowd. And we were playing some of the songs that were on ‘Boys & Girls,’" the band’s debut album.

"There definitely wasn’t this feeling of, ‘We can’t miss, Brittany’s so great, we’re going to be huge.’ That never crossed our minds. It was the antithesis of that, I would say. We felt like we couldn’t get a place anywhere."

When a nightclub called Egan’s in Tuscaloosa, a college town a couple hours south of the band’s home base of Athens, Alabama, welcomed and encouraged them, the tide began to turn. "Boys & Girls," released in 2012, eventually reached No. 6 on the Billboard album charts after netting three Grammy nominations.

The group also played ACL Fest for the first time that year, after taping an episode of "Austin City Limits" during South by Southwest just before the album came out. They’ll hit both stages again this week, taping the TV show for the second time on Friday before a first-weekend-only slot at the festival on Saturday.

It’s an expanded cast this time around, with an extra keyboardist and three backup singers added to the previous lineup of Howard, Fogg, bassist Zac Cockrell, drummer Steve Johnson and keyboardist Ben Tanner. "So there’s nine of us on the stage now — which sounds like a lot, but it’s a tight-knit group," Fogg says. "I think it adds a lot of comfort and energy."

Though Alabama Shakes’ success has made it viable to bring a larger outfit on the road, Fogg says the decision to do so was based more on music than money. On "Sound & Color," the Shakes pushed the boundaries of their sound beyond the more straightforward soul roots approach of their debut. That required rethinking the live presentation as well.

"It was necessary to bring these folks in to perform some of the new material the way it needed to be," Fogg says. "We could have done a watered-down version of this album, but the more we talked about it, and started finding people to fill those positions and doing rehearsals with them, we knew that was the band from now on."

Though "Sound & Color" isn’t a major departure from its predecessor, it feels more adventurous, like the band was eager to broaden its horizons. "We didn’t want to remake ‘Boys & Girls,’ but we weren’t purposely trying to make something far-out," Fogg says. "We were just trying to be creative as a group and see what we could come up with."

In some ways, making the first record was easier. "There was definitely more freedom, because there was no public eye," Fogg says. "There was a similar creative process, but in terms of genre, the songs were easier to categorize together.

"We’re a rock ’n’ roll band that dabbles in R&B, so that’s kind of what that record was, at that time. But this one was different. I think we wanted to expand on our influences that we’d had before. And then we found new things that inspired us. So it was harder to categorize the types of songs that we were coming up with."

That may be true, but "Sound & Color" seems to have only expanded Alabama Shakes’ audience. Early on, they were thrilled to open shows for another band with Alabama roots, the Drive-By Truckers. This year, they’ve been taking the Truckers out as the opening band on their own tour, something Fogg still can’t quite get his head around.

"It almost would have been offensive to have suggested that, once upon a time," he says. "But we have the same management, and they reassured us that the Truckers were really excited about it. After we’ve done a few shows with them as the support act, they do seem excited, and glad to do it.

"It’s surreal because we still look up to them. They’re heroes of mine, for a lot of different reasons. It was a dream come true that they embraced us and took us under their wing and helped us out early on. And I’m glad to still be able to call them friends and play shows with them. The table has turned now, for whatever reason, but we still look up to them."