This is what I am trying to accomplish, but when I have the TV set to the cable box, I only get PLII (x,m,or c) into the 970. When I switch the TV to my roof antenna, the 970 receives the DD. If the cable is outputting a digital signal via HDMI, then shouldn't the TV send that via optical to the 970 as does my broadcast antenna?
I am playing a bit of catch-up here, but it sounds like you have an optical cable running from the TV back to the 970. The problem here is most likely that the TV is telling the cable box (via HDMI) what audio it supports, and the cable box is adjusting its audio output accordingly. Thus when the cable box is getting Dolby Digital 5.1, the TV wants stereo and the box decodes and downmixes the DD 5.1 to PCM stereo. On the other hand, when the TV receives an over-the-air broadcast, it outputs the audio from that broadcast directly to the optical output and assumes that whatever is at the other end can handle it. When you see "PLIIx" at the 970, that could mean you are getting Dolby 2.0 or PCM stereo. If you see "DD+PLIIx" then you are getting a Dolby 5.1 signal and applying Pro Logic IIx to that to get 7.1.
OK. Oppo is reading Digital on the analog 7.1 inputs.
I added another optical cable from the cable box to the 970.
The 970 seems to know which input is coming from the TV, either antenna or cable, and switches automatically. Still getting digital on the antenna, but when switched to the cable box, even with an optical cable, the results are still the same as before.... Is anyone else running a Cablevision Scientific Atlanta 8300HD DVR box and having this problem?
Hmmm.... First, when you say "OPPO is reading Digital on the analog 7.1 inputs" what do you mean?
Second, the Model 970 will always analyze the incoming digital audio signal and identify what it is. The audio from your TV's over-the-air tuner will vary between Dolby 2.0 and Dolby 5.1, depending on the program. The audio from the cable box will vary between Dolby 5.1, Dolby 2.0, and PCM stereo, depending on the channel and the program.
I use an 8300HD box. One thing that may be an issue in your case is the way it handles audio output. The specific options may vary between service providers, but in my experience you have to tell it what audio output you want: HDMI, Dolby Digital, and Other. The first causes the box to output via HDMI only, I believe. The second tells it that you are using optical or coaxial digital output and want Dolby Digital bitstreams. The third tells it that you are using optical or coaxial but can only handle a stereo signal. Try selecting "Dolby Digital" at the cable box, tune to an HD channel that you know is broadcasting Dolby 5.1, and see what the 970 gets.
It will switch from Dolby ProLogic II x to Dolby Digital, depending on the source. I don't know why all sources aren't broadcast in DD, but it appears (based on input readout on the 970) that a number aren't. Commercials especially don't appear to be in DD.
You are actually getting Dolby Digital, I think, but it is only DD 2.0 and I think the 970 is reporting the surround processing mode as Pro Logic IIx. I've seen a few cases where surround processors and receivers decode DD 2.0 and treat the resulting signal as if it had always been PCM stereo when reporting the surround processing mode. Because a lot of HD broadcasts use DD 2.0 rather than creating 5.1 audio mixes, you see the 970 reporting "PLIIx" instead of "DD+PLIIx" or "DD" fairly often.