One word (or two i guess) siphon life. On all of them, with high spelldmg (think i had around 600-700 when i hit lvl 70). Getting healed for 250 every 3 secs (or i guess it was 200 per tick back then) times 30 tends to keep my hp up as long as I keep recasting every second. Tab is your friend. My imp was just there to give me a higher max hp (and later I've started using dark pact more too) and I'm sure I could have done it without him too. Healers are annoying cause they heal the other mobs, so I usually put a corruption on them in addition to the siphon life when I see them so they drop before they get too many heals off.

Note that I prefer running cathedral, though that doesn't make much of a difference I guess.
Have had some fun pulling much or all of the final building at the same time Or at least having the rest add while I'm killing the first half of the room.