Thanks for posting the manual. The whole manual is preferred to snippets. The answers are not always what and where you might think.
1) What type interconnect are you using from the DVD to the Denon? Yellow composite RCA cable, HDMI, or "S" video cable?
2) What type interconnect are you using from the Denon to the Television? Yellow composite RCA cable, HDMI, or "S" video cable?
3) Does the Denon setup menu appear on the TV?
If the answers for #1 and #2 are different, and the answer to #3 is "Yes" , I would think it's an upconversion (or lack thereof) issue.
You might want to look more carefully at the chart on page 16 of your manual. Depending on the interconnect types used, not everything that goes into the Denon comes out of the monitor.
Can you get the DVD to play when connected directly to the TV set with the same cable you use to connect it to the Denon?