Here we go again (but not on our own): off-Broadway smash hit Rock of Ages is flexing its musical muscles, gearing up for a Broadway transfer that would make the rock gods of yore proud. The not-just-another-jukebox tuner, which starts previews on March 20 at the Brooks Atkinson Theatre, hit us with their best shot on March 3, showing off head banging hits like Whitesnake’s “Here I Go Again” and Poison’s “Nothing But a Good Time” at an open rehearsal (which really was a good time!). After strutting their stuff for the cameras, stars Constantine Maroulis, Amy Spanger, James Carpinello, Mitchell Jarvis and the rest of the ROA crew kicked back for a funky photo op, schmo