Easiest way I took care of this boss is to run my DK right up to the boss from the left side (so the adds have to run through the boss to hit your guys) and make sure my shamans follow right up behind my DK at standard follow distance - just leave them on follow.

Then, use a castrandom or something that rotates between LB and CL. Drop all your fire elementals. Between CL hitting the boss and reflecting to adds/frost tombs and the fire elementals none of your guys will stay in tombs for more than a couple seconds and the adds will be dropped super fast. Makes it cake.