Nearly 8yo 1050 running as a pre-amp in stereo mode feeding a pair of ~4.5yo M200's which each drives an Onyx Rocket RS750.

Inputs:
OTA & QAM TV (coaxial audio)
CATV DVR (optical audio 1)
DVD player (optical audio 2)

Recently, just within the past 3-4 months, I've noticed the right channel cutting out when watching TV via the DVR. The lights on the M200's stay green. If I crank the volume up to 45 or better (I normally watch/listen with it set at 27-30) I'll usually hear some crackling and then the audio cuts back in. It sort of "feels" like something plugged and I'm "blowing it clear", but this is all electronics and that's simply not possible.

No cables nor boxes have been touched or moved in nearly a year, so there's no "recent changes" that may have precipitated this behavior.

The CATV DVR box has option to set optical out to "Dolby Digital" or "PCM" ... problem occurs with both settings. CATV DVR box is a new replacement as of 2 weeks ago, the prior one was fried, according to the cable tech, "by a problem with the line levels on the street".

I can't remember this happening when watching OTA TV or DVD (both fed via different inputs), nor when listening to the radio or CD's (which are played on the DVD player), but I watch them *far* less than I do HD content off of the DVR, and I may simply not remember it happening. (hey, watch it! I'm ONLY in my 40s!)

Seems like a lot of variables. And a lot of different things I could swap, but ... based on the above, what would be the most likely source of the issue and therefore would be the most likely place to start my testing?

Should I swap the M200's and see if the left channel starts dropping out instead of the right?

Should I swap the DVR and DVD optical inputs (means reprogramming the remote)?

Should I bring the 950 up from the HT and sawp it in for the 1050 as a whole (big pain in the neck w/wiring and remote programming)?

I've been "dealing with it" due to the overwhelming aspect of the last option above ... I just don't want to deal with all that right now. SO ... any suggestions as to how to best optimize my search for the problem?

Thanks for any suggestions or ideas!