i haven't looked at the hd radio mods in a while, but here is what i try to remember:
the ground mod was when you placed a wire between the ground power connections and the negative rca lead right? don't know if this has any effect, just checking that i am on the same page.
also, isn't there a command to turn the volume down on the hd radio?
i think that the volume might be too loud on the hd radio for the selector(at work, i have 2 computers, and one set of speakers, so i send 1 computers audio into the aux jack of the other computer-- if the computer that goes through the aux jack volume goes above 1/2, it outputs horrible distortion).