OK, here's what I now know:
At one point my newest (not new but new to me) Onkyo receiver would not play quad correctly.
After a firmware update, the Onkyo plays quad.
My BDP-103 & my DV-970HD (freshly returned from Oppo service) both play quad just fine via the Onkyo.
The BDP-80 plays only front channels from quad at this time.
What source I am using to test:
A DVDA disc I authored with a few quad songs.
I got in touch with the Oppo service folks and we swapped emails Friday afternoon until we basically ran out of time.
After asking about my setup and particularly the receiver, they sent me a firmware revision to try, but alas it did not help me.
At this point I've done about all I can do, I think, including factory reset, removing power from the BDP-80 for >30 minutes,
and any other suggestion the service folks have made.
I could be and am frequently wrong but I don't believe the service folks have seen this particular problem from this player before, so I keep hoping
it's not a hardware problem.
I hope to resume the conversation with the Oppo service folks Monday and maybe something good will happen.
Not really germaine to my problem, but Oppo service received my ailing DV-970HD last Friday afternoon, replaced the decoder IC and the transport and had it back out the door headed my way the same afternoon. I don't see how you can beat that kind of service!