Cable Box Digital 5.1 converted to Digital Stereo

Did you try the analog outs from the cable box?

Having the TV on is not so bad. It tells you what is playing.

Oddiofyl- Did you try a co-ax ground isolating transformer between your cable box and the incoming cable feed to see if you can get rid of the ground loop? You can get one cheap at Rat Shack (if they're still open) or in a pinch you can put two of those old 300 ohm to co-ax converters that came w VCRs (remember those?) back to back. Cable feed to coax converter-twin lead to twin lead-coax converter to cable box. If that seems like a good idea and you can't make sense of what I am trying to say, pm me through agon and I can send you a sketch.

However, I agree w Kal that you hit the point of diminishing returns pretty quickly on the audio in the cable feed.

Yeah, I can use the Cable analog outputs, but I thought with a digital output through my Dac I could obtain better sound.
I'll check with Comcast about the Xfinity one box. However, past experience tells me that will be a hassle getting through to someone that's knowledgable.

Ozzy, on the Xfinity box you need to go to the menu and select 2 channel audio (PCM). Run an optical cable from the Xfinity box to your PS Audio DA converter - less jitter with the optical. I run this way through my Oppo BD-105 with good results. Some of the cable Paladia concerts are really nice. You may decide to stay with 2 channel after you do this. Good luck