I haven't seen this degradation of the sound quality, and I've used the 970 for hours on end. I use it mainly for watching DVDs or listening to CDs, however, so I wonder if the problems you've experienced could be due to the auto-polling of your cable or satellite signal. Since you say that the Dolby mode must be "recycled", I'm wondering if for some reason the 970 loses its lock on the digital signal.

I'm having HD digital cable service installed tomorrow (finally), though, so maybe I'll see the answer for myself sooner than I'd like ...