Yea, the original author who wrote this only put in support for the vt1165 voltage regulator, and the 6990s don't have that. My 5970s and 5870s have it. Basically, if you get "Unsupported i2c device (00)," then your card has a different VRM and won't work with this (unless there is documentation somewhere showing how to access those VRMs in a C program like the 1165, then we could add in support).

So, to clarify, if you run radeonvolt and you get NO output at all, the changes I made to enum_cards should track down that particular problem. If you get "unsupported i2c device," the changes I am making aren't going to help for now.