When attempting to kill him you don't need to knock him down, when he reaches his damage limits, if you have a sufficient amount of life stealing right?
that method of killing kanaxai is a lot more difficult than the new improved tactics.
Lure Kanaxai to one side and KD him two times to let him spawn 24 shadows.
Again lure him to the other side away from the shadows and body block him in. KD him all you want and no more shadows will spawn.
You don't kill any of them - there can only be 24 creatures spawned from Kanaxai KDs alive at a time, so if you leave them alive, KDing Kanaxaia won't spawn any more.