Well, here's the thing. As most sites like that do, they are overcharging you for underpowered parts. It's not a good deal, and you could make a MUCH better system if you built yourself. Would you be willing to look at doing that?
Also, why Nvidia preference? It's fine, just curious. Right now AMD has an upper hand in the gaming sector, due to better bang-for-buck.
If you could answer those questions I think we can get started
Here's what I'm thinking
Gigabyte Z68 mobo
-2 GTX 570's. Yes, 2!