Denon publishes their serial/tcpip commands in documents like this:
[Link: assets.denon.com]

Unfortunately, they can be somewhat hard to find; and in the short time, I did not find any document officially supporting your device. However, experience has shown that the commands do not change that often.

I have a Denon AVR-A100 myself, that I can control over serial (RS232) with a GlobalCache serial port, using this homemade (unfortunately museum ripe): [Link: github.com]

Does this help?