"High performance" power mode = SLI. Unfortunately the default power setting is "balanced". That mode runs one video card until it detects an app requesting 3D graphics and then it switches to SLI.
I have 2 7900 GT's in SLI on my system. Is there a way to have my cards to be kept in SLI mode and to be able to output to my HDTV VGA connection? It seems that if I want to output to my tv's vga port ...