Have one infiltrator for cloack: it will be needed for objectives outside the room.
I have it done with engies, infiltrators and even a Turian Sentinel that beat my score at the end. But no soldier, adept or vanguard. I always go Salarian Engineer because I'm very confortable with him and a set up that keep me 200% recharge rate. Power are more important than weapon because both Energy Drain and Incinerate are more powerful than any of my weapons.
The trick is to chain overload / energy drain + tech burst the shit out of the wave of geth coming. Salarian Engineers shoud spam Decoy every 20 to 30 seconds to crowd control the flow and draw fire away.
People should stay in the room. Some tend to go in the back (to snipe safely and avoid rumble from the chaos : it's okay. Some go of the right, outside : it's not okay because it's hard to get them is they die.
Enemy very rarely spawning behind you. I don't say never because, once in a while (twice a match ?) I got flank by a geth. Did he spawn behind or just moved around ? No idea.
Hard part are when Geth Prime really get into the room (two can be a problem) and start to flank. Other than that abuse cover, spam energy drain/overload/incinerate, refill in the back if needed, and don't forget that a pyro charging you is dangerous but if you're in cover, you'll grab him before he can really hurt you.
It's really easy, really. Just stick together and unleash tech hell. Even for wave 11. Don't move out until it looks clear (between the last minute and the last 30 seconds) so you have time to clean a bit if the way isn't clear but not too soon to not get overrun.
