Twin leads, two drummers, an impossibly soulful vocalist — no American band ever emerged with the sheer power of the Allmans. It’s the tragedy of these terrific players that, ever since the long-ago deaths of Duane Allman and Berry Oakley, their albums have only echoed — clearly or confusedly — their original boom. This time out, Gregg’s world-weary singing and guitarist Dickey Betts’ country inclinations get subsumed too often in formula blooze. But there’s no denying stellar jamming. Give the Brothers any obvious three-chord sequence, and they soar, spinning solos and building percussive thunder.