OK, let me add that I have KEF LS50's with a KEF 8" subwoofer. The LS50's sensitivity is 85dB, so not the most efficient speaker. But not that bad either. I listen to music at a very reasonable sound level (around 70dB at the listening position).
When I listen to music I use the Denon's very handy "Quick Select" mode to turn off Audyssey's DSP. So, I listen in straight 2.1. Music is noticeably clearer and more detailed with DSP off.
Sounds like (no pun intended) that the Denon is fine and that if I wanted better SQ for music I should look at different speakers, maybe something a little larger with more "impact". Actually this would be good news as I really like the Denon and the Heos app.