Fighting Tartarus without fighting Brutes

There is a way of fighting Tartarus without fighting all those brutes before the cutscene, thus conserving ammo. This tactic is extremely simple. All you have to do is after Johnson blows the door, fly to the right and go inside the circle thing 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 isn't there just throw a plasma grenade at the four brutes, then ride that platform with Miranda Keyes and blast Tartarus with all that ammunition you just saved.