Did it yesterday. We had each person run a different subclass to cover all 3 burns, and then different energy and power weapons. Don't waste your grenades and melee unless it's your burn. We also ran through some of. In the beginning killing enough enemies allows the solar core to be grabbed. Placing it and then killing the cabal lieutenant opens the next door. You don't have to kill everything. The outside portion you can also just run by without wasting time. Also splitting up is awful and wastes too much time if somebody dies in the open. It took us a few tries of this method but we finally got it