I'm going to throw my two cents in here, even though I don't know that much about ground loops.

When I got my 950/770 combo, I had a loud hum coming from the center channel. I talked to Scott and he told me how to isolate it. I finally figured it was what you have, the cable outlet. He gave me some fixes for that, but they didn't work. I would eliminate the humm, but also the cable feed. Finally, on a wild try, I bought another, what I would call, inexpensive ($40)surge protector. I plugged it into its own recepticle and plugged the amp into it. All the other equipment is on another surge protector plugged into the adjacent recepticle. Guess what? No more hum. Dead silence. I can't tell you why this worked. Theoretically, they're on the same circuit, I think. But, it might be worth a try before you start putting big bucks into this.
Ron