I run your same setup and had quite a few problems with him as well. I did manage to finally kill him, though, by having each of the shamans toss a quick heal on themselves and then go right back to DPS'ing so that my primary healer didn't go oom. Kill the orbs asap and get back to DPSing the boss. I used mana tide when I got to around 50% mana and popped heroism & fire elementals when the boss got to around 40%. The time I finally killed him, all my shamans had died and I finished him off with my pally (Lay on Hands).