Hi Hiker54,
I have the same problems. I own a Denon A11, which is the same as the 5900. I can't play any dvd-audio from the Universal classical labels (Philips, Decca, DGG) The readings on the display are the same as yours. The only way to play this discs is the dvd-video mode.
I am already waiting 3 months for a solution, but the Belgium Denon importer is not very cooperative and that is the least one can expect for a player which costs in Belgium 2499 Euro.
When my dealer had another A11 in stock he let me try it out without succes. So I think there are a lot of players sold with the same defect as ours.
I hope the problem will be solved in the firmware update which is still not available for the a11.
Anyway I send a link to this thread to my dealer and to the Importer.
Maybe who more of us who complain, about this problem, the better the chance it will be resolved.
Greetings
Gromit