This guy has a NASTY innate damage shield that does around 800 heat damage at 7k heat resist.
Have the MT fight this guy -unarmed- and just taunt the entire fight. Have melee and casters just range this guy to death. It is a slow burn fight.
You can probably melee if you have high enough resists, as you can resist some of the damage shield hits. Also, using a slow weapon (>2.5) will prevent you from taking too much damage.