I got another tactic for the "to the ground!" Achievement.
This needs a hunter.
CC 1 of the adds by letting the hunter put a freezing trap in front of one of the doors just before the adds come, nuke the other down and then switch to the boss and nuke him.
Just before the second adds come (Add 3 & 4 or 5 & 6 if you count the first 2 adds), Let the hunter put a trap at the other door, and again nuke the other one down and go back to the boss.
By the time that the first one gets released from the trap the boss is down.