Although rumors continue to buzz, Metallica and the Beatles aren't headed to the "Guitar Hero" franchise just yet, according to Kai and Charles Huang, the sibling founder of game publisher RedOctane.

Speculation abounds that Metallica will be the next band featured in their own version of "Guitar Hero," much like the just-released recent Aerosmith-centric game.

"We're not ready to comment about Metallica yet, but what I will say is that we'd love to work with all of the top rock bands of all time, whether it's Aerosmith or Metallica or AC/DC or Led Zeppelin," Kai Huang tells Billboard. "If we get an opportunity to work with those bands, we would love to do that."

As for reports that "Guitar Hero" is in discussions with the Beatles to bring their music to the game, Kai Huang would only say, "Unfortunately, those are rumors right now and we don't have any comments yet."

"Well, I don't have to tell you how difficult it is," Charles adds. "Everybody in the world has tried to get the Beatles to put their music on all kinds of different platforms, and it certainly would be exciting, but it's also a difficult challenge."

Next up for the franchise is "Guitar Hero: World Tour," which for the first time adds drums and vocals to the mix in a bid to compete with rival "Rock Band." An added twist for the expected fourth-quarter release: The game's "music studio" feature allows users to compose and record tracks and share them online.