When I had the 990, I pretty much left it in Dolby Digital II mode with the 6.1 speaker mode turned on (occasionally for DVD's, I would manually switch to DTS). The 1050 would automatically adapt when a 6.1 signal was present and send power to the speaker if it was, otherwise the speaker was dead quiet.

For cable TV input (from the SA-8300HD) over digital-coax, it seems, I would simply configure the input to Dolby Digital Ex. This should result in the same signal going to both rear surrounds so wiring just the left output, would provide the output if preset. This assumes of course that that mode handles a regular 5.1 signal. Any ideas if this is correct? Is there any reason to consider using PL-IIx movie?

I am much more confused about how to perform the configuration for DVD's. I am sending the signal via optical to the 990 via optical and letting the 990 decode. I have not had a chance to experiment yet.