We killed him for the first time this week, it was pretty intense but it didn't really take us too many attempts. (And one of our healers wiped us at 5% while tunnel-visioning with a bomb during tantrum =x.)
I guess some people don't use a tank at all on the sparks, but we found things were much more controllable that way because they hit pretty hard if they get onto a clothy.
We used 6 healers (+ a ret paladin, of course...)
Holy Paladin, Disc Priest, Holy Priest, 2x Resto Druid, Resto Shaman.
Holy Paladin + Disc Priest on the main tank (though the Disc priest switches to raid heal during tantrums)
BoL + Raid healing druid assigned to keep an eye on the offtank.
Resto Shaman assigned to focus solely on people who have bombs, especially during tantrums.
Everyone else was on raid healing, unless they were needed to cover for another healer. The disc priest switched to raid healing during the tantrum as well.
I think from the healing perspective the most important part was to ensure the assignments are covered when a healer has to run out with the bomb, requiring clear communication. Several of our healers were struggling with mana by the end.
I believe for dealing with the sparks we had specific ranged DPSers who were responsible for burning it down, while the melee and several of the ranged who were in classes that aren't so great at target switching stayed on XT. Our spark uptime was nearly 100%; I understand some people have burned them down faster to reduce healing load, presumably at the expense of some frictional dps loss on XT-002, but this worked alright for us.
Here are our breakouts. Nivwar was the main tank, Revenir was the offtank. You can see we had quite a bit of help out on him with druids, partially when his assigned healers were moving and partially when they had GCDs to spare.
http://wowwebstats.com/6btdeoikbdk6e?s=424042-592573