I have a 5.1 system that includes a denon 2307ci, bose speakers, martin logan sub and a comcast motorola dvr(not sure what model). The dvr is connected to the receiver through digital coax. When the receiver is in Auto (it displays "Dolby Digital") and im watching the HD channels, on certain channels I only get sound when the program is playing, not the commercials and on certain channels I dont get sound at all. If I switch to 5ch stereo the sound works. So far i've only tried changing the coax to optical with no luck. Im going to try swapping the dvr out in a couple days but i wanted to if anyone had any suggestions.

Tv programs and commercials are not all 5.1 and that's why you get audio dropoiuts.

Tv programs and commercials are not all 5.1

True, but if the receiver is set to "Auto", it should switch between 5.1 and stereo automatically...you shouldn't hear silence.

The OP is on the right track checking with the cable company. It may be a bad cable box or low signal strength coming in your home.

Yeah, probably the box. I have a STB connected with only a coax and I get sound on everything. It isn't always 5.1, but it's always there.

This is why I was confused. When in auto it should switch between stereo and 5.1. I swapped out the dvr and everything is ok now. Thanks for the input.