Losing Surround Sound and Volume

I have my Comcast cable come into my Tivo Premier using M cards.

The Tivo then feeds my Sansung HD TV (less than 4 months old) via HDMI.

Then the TV feeds my surround sound amp via Optical cable.

So when I installed the TV, sound was great. Sound sound on most channels and I could set my TV about -40db for volume.

Now I seldom get surround sound and the volume needs to be 25%-40% higher to hear dialogue.

Now I suspect it is compression issues with Comcast but before I try that fight, is there anything else I can try to identify the issue?

I could not find any settings in my Tivo to check or set sound.

Thanks

Art