HDMI audio or 8 channel, which is best quality?

Depending on the quality of your CD player, you might try digital into your Sunfire. I use my Oppo as a CD player, though.

That's a good idea. I'm not at home to check it right now, but I think it has digital out, and if I remember rightly it's optical. It's a Sony 300 disk player, 2 or 3 years old.

For cable boxes, I usually recommend (and the only time I recommend) TOSlink. Cable boxes are notorious hum generators, and optical provides the isolation needed.

You should only get a hum problem if cable service to your home does not share a common bond, as it should. Toslink can be effective for circumventing the lack of a common bond, but it would be best to ensure proper bonding anyway. A cable box does not inherently produce hum.

Here's my favorite HDMI article: http://hometheaterreview.com/what-if-hdmi-actually-worked/

Rodney, tat's true. Cable boxes aren't inherently noisy. The grounding and shielding of all the cable from A to B is what the problem is. Too many different people working on it without proper supervision and lax standards.