Since this is almost a new custom build, have you stress tested the new setup yet? This would be a good way to see if your PSU is up to snuff. Check
this link for a list of utils you can use. Keep an eye on your temperatures as well during these tests (Intel TAT). See if your PC is stable to run these utilities. (forgive me if you're familiar with all this stuff)
Otherwise, you should also start eliminating the culprits. Does the PC crash when playing other games? Try uninstall the audio card completely and use the onboard only. The mobo also has onboard video you could use instead of the 8600gts, but I dunno if your games will even run on the onboard...worth a shot though to see if it's related to your card.