I think i did it at 512. The most important advice i can think of for this boss is take your time. I died plenty to retarded stuff, like eating the chaos bolt/"forgetting" that the hounds spawn etc, when just tunneling the boss. So take it easy'ish.
So here's few things i noticed/found online.
When the boss starts to summon fel hounds, move your pit lord to the left side of the gateway, cast rain to the gateway and move to the left. Havoc+CB the first 2 hounds and use the charge+flames on the third along with your nuke.
Before the doomlord spawns(or during the summon), re-enslave the pitlord(i had a macro to dismiss it), then charge+flames on it and soulshatter and you don't have to worry about the doomlord anymore during the fight.
Remember to re-cast your tele as you have to use it due to the 1min cd on the gateway.
And most of all, don't give up on it. At worst, get few more pieces of gear and kick his a$$. :P
*edit* i also specced to unbound will and pretty much kept it on cd along with imp dispel from the GrimSac.