However...
I have COX Cable digital, and a Scientific Atlantic box.
If you go into programming and select a future TV show for a reminder to watch later, the digital audio signal of the current program becomes limited and sounds very compressed. I found this out by accident going from no program in waiting while watching a concert on Palladium in Dolby Digital to setting a program to watch later,
then taking the reminder back off. There is an extreme difference in sound quality and volume. (Volume had to be moved from -25 to -16!) And the compression becomes intolerable.
I was since told DVR programming can effect this too.
Try this with your set up, you may have to have no reminders, programs, etc in waiting to get best sound. Probally bandwidth issues.