Aye, if you're worried about performance bite the bullet and get an EVGA Classified 4X SLI and another couple of 480's. Or, an SR2 + new CPU's + 2 480's. If you're doing this for somebody I hope your business arrangements aren't so that they'll be pissed over the cost of this whole thing. If I had the cash I'd shell out for this 3D surround stuff in a pinch. But then again, who has the cash? Regardless, I'd be like Ho-ly-cow...
As for the cooling, add more fans to the cabinet; the bigger the better. An array of 120mm's might not do the trick unless they're high-end 38mm's, and even then those have to be pretty badass. Don't hook them up to the machine inside, just grab a cheaper PSU like OCZ or something to power them, then jump it.
You may also want to consider W/Cing, but then again if this is to be used in a lounge it might be risky if something either goes wrong or the maintenance happens to be a bitch. Some self-contained, CoolIT-type solution may be what your after. I'm pretty sure you can hook them to GPU's if you get proper blocks for them.