For smart metalheads, Christmas comes early in the form of one of the best heavy-music lineups all year. Topping the marquee is Sumac, the post-metal supergroup almost unfairly stacked with Aaron Turner (Isis, Old Man Gloom, Mamiffer), Nick Yacyshyn (Baptists) and Brian Cook (Russian Circles, These Arms Are Snakes). Their expansive sound comes in staggering odysseys that exist beyond metal convention.