Coming from the broadcast engineering side.. I agree, bumping up the center channel is a good option. Generally, for productions originating in the USA, the center channel will be only dialog, so this will work.

I can confirm that in the audio mix suite of the studio or production truck the sound mix is superb. Unfortunately there are many places this can go wrong, starting with static dolby metadata that is overwritten at some place in the broadcast chain resulting in a mix the engineer had not intended. Mostly we have settled on static dialnorm of -24db, but this still varies some and can cause this problem when the dolby metadata is overwritten with the wrong value, confusing the receiver on how to mix in the center channel.

The cable box can also introduce additional audio processing making things worse. I'd double check that anything that sounds like an audio "feature" in the cable box is turned off. Be sure the box is set to pass the audio bitstream without any additional processing.