I’ve been working on an MQTT interface for Denon (and Marantz) AVRs and it is now stable enough to share:
It supports discovery of the names of the AVR, zones, and sources via the web interface, but uses the TCP/IP (telnet) interface to communicate with the AVR. It currently runs as a stand-alone process outside of HA either via docker or node.js.
Then I made a companion command-line (node.js) utility that automatically registers devices for each zone with a set of entities useful for setting up a universal media player. It also generates a yaml config file with a universal media player for each zone.
Here’s an example of the entities that get created:
