Just in case anyone else is stuck on the 2nd boss in Shadow Lab, here is what I had to do:

I had to buy a 2nd set of gear for my 4 DPS toons. It turns out that I had way too much DPS and too little health to survive the Incite Chaos. I ended up buying a bunch of Elder/Eagle/Stamina gear from the AH for each toon and it didn't really cost that much. Maybe 100g each, if that. I went from about 5k health to about 8-9k health each. Then I just parked the 4 dps at the back right edge of the closed door he guards and it went reasonably well. Just make sure to heal up between each Incite Chaos. Don't worry too much about drawing aggro with healing. If you use Shaman like I do, he doesn't hit too hard on chain.

After killing Blackheart, it was ironic how easy the last 2 bosses were. I easily one-shotted them in my normal gear. (note that this was all on normal, not Heroic)