The first boss really isn't bad if you have decent positioning. You have to tank it where your tank is on the "armrail" of the stairway facing out at a 45 degree angle. Have the boss completely off the stairway at that 45 degree angle and his arcane bombs will very rarely make it up to your dps on the stairs (still spread them out a little, but I kept them close enough to still chain heal each other). I also had better luck using a dedicated healer here because of mana issues on the guy trying to heal and dps. It's a simple tank and spank if you can keep those arcane bombs away from all but the tank.

If you want to farm totem of the void you dont need any bosses, just the 2 mini-bosses which are tank and spank. They do enrage and hit pretty hard though, but nothing a decent group cant handle. Go to the right first, clear trash, kill miniboss for the first crystal, come back to the entrance and go to left, clear trash, kill the second boss, combine the crystals, go down the stairs, clear the mages/bot there (they sometimes aggro and sometimes don't when you're at the cache) and you're done.