Then, without a Denon myself. I am stumped.

Maybe I missed it, but have you checked that the Panny is set to output to a 5.1 setup? Maybe it is downmixing everything to 2 channel. One way to check is to look at the speaker set up in your player and make sure the picture shows 5.1 speakers, with each set to small.

And can you confirm whether the lights come on when you change from a cd playing from the DVD player (2 speakers should light up), a dolby digital DVD (6 speaker lights should come on, along with the DD symbol) and a DTS track (again 6 speakers should light up, but the DTS symbol should show).

That should eliminate source set-up issues.

Once that is eliminated and the above suggested speaker switcheroo is tried, then the problem can be isolated to the DENON (or not), which will make it easier to diagnose.