I was just thinking this group composition would be the best, and wanted to be in on the run ;P
Actually I would suggest using caster dps. Unless you're stacking tanks with the melee buffs/debuffs. It's a fairly small room but the bastard hops around alot (the fight benefits ranged classes).
Alternative group idea:
Unholy dps DK (OT)
critchicken or ele shaman
Healer (doesn't really matter. I'd go with a priest)
A good majority of your damage is magic based now (including both tanks) allowing your ranged to do full time nukage while Archavon dances around. DK's provide the ebon plague debuff and the ability to put out decent damage while off tanking (tank spec, dps gear).