Have you tried downloading the most recent AMD driver 12.3? I started with 11.9 then recently switched to 12.3 and, at least with DiabloMiner, I do not have the CPU core utilization bug with a 5870 and a 5830. Also both cards are detected at Windows startup so there's no need for dummy plugs. If you give it a shot, I would completely uninstall your current driver version and the SDK. With 12.3 you don't need to download a separate SDK, just use the one included in the main installer. Good luck!! Let us know if you get it working.