Utilizing all my cores and GPU's for F@H?

Basically here's the situation, I have an overclocked dual core and 2 3870's in Crossfire, and I want to be able to utilize them all effectively in F@H, but it doesn't seem to be happening. I downloaded the GPU client, but from what I hear each client will only utilize one GPU and one CPU core, and needs to be configured to use multiple GPU's which I'm not sure how to do. Also it says Crossfire will reduce performance, so do I need to disable Crossfire when I'm not gaming?

It looks like the ideal situation would be to run 2 GPU clients, since each appears to use one CPU core as well, I know of course how to set processor affinity but how do I go about assigning each client to each GPU? All the info on the site seems to be outdated...