There's something about the traditional Broadway musical that feels, well, staged. Even the deftest directors can't conceal the inherent, disruptive artifice of characters bursting into song. That's what made Actors' Playhouse's production of this rock 'n' roll road show so unique. Million Dollar Quartet, which imagines the rollicking music, humor, and infighting of a studio confab among Johnny Cash, Elvis Presley, Carl Perkins, and Jerry Lee Lewis, is in its own way as whimsical as people-gobbling plants and demonic barbers. But artistic director David Arisco's naturalistic direction and his cast's remarkable verisimilitude overrode the perception that we were watching a fantasy. We were eavesdroppers of an apocryphal hangout, witnessing four legends shoot the shit when they didn't want to shoot one another. And it was a loud hangout: The songs, arriving organically and ending with little fanfare, had an amped-up, raw imperfection that seemed to filter from the convincingly accurate onstage recording booth. The production was another reminder of the boundless creativity Actors' Playhouse can achieve in its flexible upstairs venue.