To call My Morning Jacket a post-jam band is wishful thinking or splitting hairs. On the new double-CD set Okonokos, they jam all right from drum solos to bass babble to guitar psych-wank and the only thing "post" about them is occasional rhythmic woodenness. But there's something magisterial, even evocative, in their labors, like that of a band fighting for its life in a heaving, oozing mudslide of sound and yet still getting its rocks off, still finding transcendence through sheer drone and lead singer Jim James' sky-high, often pretty bay. MMJ's last St. Louis appearance (at Mississippi Nights) started out loud, advanced to deafening and ended in pain. The band's return is neither for the faint of tympanum nor for the deficient of heavy-rock wonder.