Re: power supply strong enough.
I seriously doubt it. I took a gamble a while back with 15A on 12V using much less power-hungry components and BOOM! Fortunately it didn't take out anything else; I got extremely lucky. NVIDIA recommends at least 23A on the 12V rail for the 8800GTS's, but you probably want even more since you're getting the Quad.
Good luck with the xbox build though, sounds unique.
ASUS A8N32 SLI-Deluxe, AMD Athlon X2 3800+ @ 2.8GHz, eVGA 8800GTS 320MB, 2GB Corsair XMS DDR400, 160GB WD HDD + 320GB Seagate Barracuda 7200.10, AC Freezer 64 Pro, 700W OCZ GameXStream, NZXT Zero :D
I think I've decided to leave... maybe I'll come back sometime.