Cable Ground Isolator & HD compatibility

So I'm getting the dreaded hum due to a ground loop. It's definitely the Cable TV connection. However, the only connection into my audio gear is via an Audioquest 75 ohm digital interconnect into AV receiver, which is separate from my main 2-channel setup. I only have hum problems when I connect the cables between the AV receiver and my 2-channel preamp (for the main channels).

So here's the question(s): I could isolate the ground at the RF cable coming into my High Definition cable box, but then I hear stories about bandwidth and HD compatibility problems. I could also isolate the ground on the 75 ohm digital cable, since that's the only one going to the AV receiver (and causing the loop with electrical ground). However, I would then worry about making other connections in the future and restarting the whole problem.

HELP?....