I've gotten an MSI R9 280X flashed (thanks Mr. Zarniwoop and everyone over at Netkas) and running like a champ in my 2006 Mac Pro. It's working so well that I decided to try to set up a crossfire setup (for gaming in Windows). I have a second MSI R9 280X, and bought a Seasonic 600W external PSU to power the cards. Both of the cards work great individually, but as soon as I hook them together and try to enable crossfire - instant BSOD. I've tried the latest Omega drivers, the most recent beta drivers, the Boot Camp drivers from early last year - none of them work. Has anyone been able to get this to work? I (somehow) managed at one point, and it was working great; almost a 60% improvement in framerate; but I had flashed the first card but not the 2nd, and connecting them messed up the display on "About This Mac" somehow. I decided to get clever and flash the 2nd card too, and ever since then I haven't been able to get crossfire going again. Frustrating. I should have just left well enough alone.