For sure the shaman help. Are you dispelling the holy fire dot and dispell/spellstealing the renew? That really helps when you're first hitting this encounter.

Black Knight, one thing: his desecration, mark, and ghoul explosion are shadowfrost dmg, which means will resist against whichever of those is the lowest. So run cold resist aura and prayer of shadow protection both. This helped me a lot early on.

Keep at it though man, that group can definitely do it. PoM and CoH are great heals for this encounter.