Luka Šulić and Stjepan Hauser are used to moving between different worlds, the Croatians known as 2CELLOS as comfortable in the grand concert halls of Europe as they are hanging with rockers Elton John and Steve Vai. But there’s no disputing which musical world has been better to them in terms of finding an audience.

Although the collaborators were first known as classical-music prodigies, they’ve become stars by giving the cello treatment to songs you’re more likely to hear on CFOX than on Deutsche Grammophon. Celloverse, the duo’s third and latest release, features heavier-than-heavy tracks by the likes of AC/DC (“Thunderstruck”), Iron Maiden (“The Trooper”), and Radiohead (“Street Spirit [Fade Out]”). Forget vocals: the record captures the beautiful bombast of the originals on, naturally, nothing but two cellos.

Reached on tour in Southern California, Šulić acknowledges that classical and pop songs present different challenges from a technical standpoint. But there’s no question which genre is more taxing, the payoff being a tour that’s currently selling out soft-seaters across North America.

“I would say that it’s definitely more exhausting playing pop and rock songs,” Šulić says with a laugh. “You sweat more and you really have to give it your all. Last year we had to cancel 16 of our U.S. shows because Stjepan had a neck injury—he had a disc hernia where a disc came out of his neck because of too much headbanging. So, yeah, playing what we do is more intense and tiring than playing, I dunno, Bach.”

Sometimes, however, the goal is to bridge the two worlds.

“It depends on the song, but if we play a U2 or Coldplay song, we play it in a classical manner,” Šulić notes. “The nuances and dynamics are things that we learned playing classical music.”

After occasionally crossing paths at cello recitals and camps during their formative years, Šulić and Hauser found themselves studying in London, England, at the turn of last decade, both on track for the classical circuit.

“We both come from musical families and had really rigorous classical training,” Šulić reveals. “We studied abroad in London, Vienna, and Manchester with great teachers in great schools. We also entered and won many classical competitions. We were seen as up-and-coming classical musicians who were trained to be soloists, to be chamber musicians. Somehow, though, we never had a project together until 2011. But we always felt, because we are so strong as individuals, that if we did something together it would be really special. And we were right. The minute we joined forces, it just exploded like it was meant to be.”

The rise of 2CELLOS would start with Šulić and Hauser getting together to film a one-off video for a cover of Michael Jackson’s “Smooth Criminal”. Featuring the two musicians furiously duelling on their cellos in what looks like Croatia’s regal Diocletian’s Palace, the clip quickly went viral on YouTube. (It sits at over 18 million views today.)

Before they knew it, the two were guesting on The Ellen DeGeneres Show, doing guest appearances on Glee, and generally becoming pop-culture phenomenons. Even before the blizzard of attention, the men of 2CELLOS realized they were onto something by reinventing hit pop and rock songs for cello. The big challenge, though, was proving they were more than one-off YouTube celebrities.

“We knew we had a really great arrangement of ‘Smooth Criminal’, and a really powerful video,” Šulić says. “And we knew that it would get attention from people, but we didn’t expect it to blow up so quickly. Or that we were going to blow up so fast—we only had that one song. That was the breakthrough, but then the real work started. We had to develop from a YouTube sensation into recording musicians and a serious live act. There are many YouTube sensations, but if you don’t build things up and work hard after that, everything goes to waste.”

Šulić and Hauser are fiercely committed to refining what’s made 2CELLOS famous. Having found that collaborating with Sky Ferreira and Elton John on 2012’s In2ition seemed like a departure from their roots, the two musicians went stripped-down for Celloverse, holing up together with nothing but a laptop and their instruments.

“The first album [2011’s 2CELLOS] we did in Croatia and it was self-produced,” Šulić says. “The second one felt like we did it too soon—we still had so much exploring to do of our sound. With this one, about half the album was recorded in Las Vegas in a hotel room. All the hits we do, like ‘Thunderstruck’ and ‘The Trooper’—the videos with the most views on YouTube—were all recorded in the hotel room, which is crazy. All you need is a vision of how it should sound. Anything is possible today with a laptop—you don’t need fancy studios. Or equipment. We realized that the less production we have, the more successful our songs and videos are.”

The only time 2CELLOS isn’t interested in cutting back is when it plays live. Then, Šulić suggests, it’s time to go all-out—at least until discs get herniated. 2CELLOS may have started on YouTube, but it’s since become famous for proving that taking the stage with nothing but two cellos doesn’t mean you can’t put on a show.

“We’ve really worked on finding a way to play all of our arrangements live and making them attractive,” Šulić says. “Our arrangements are very demanding, and technically speaking, there are only two of us on-stage, which can make things hard. It’s really hard to entertain when it’s just two of you. Our shows are really intense and exhausting, because we have to play all the time, and then entertain while we are playing to really large crowds. It’s a constant process of learning and keeping it fresh.”

2CELLOS plays the Queen Elizabeth Theatre on Friday (April 15).