Fighting Tartarus without fighting Brutes

There is a way of fighting Tartarus without fighting the Brutes before the cutscene, thus conserving ammo. This tactic is extremely simple. After Sgt. Johnson blows the door, fly to the right and go inside the circle formation that is connected to the building. If done correctly you should skip straight to the cutscene with Tartarus and, if you are lucky, the Banshee will be sitting in the hallway behind you. However if it is not there, throw a plasma grenade at the four Brutes then ride that platform with Miranda Keyes and blast Tartarus with all of the saved ammunition.