I have been looking at this a little bit as well. I have a Marantz unit that is remote controllable though telnet. The Denon binding works well if you have one of the units that are a little bit older. Marantz/Denon changed the protocol a couple years ago. I have the full spec for the telnet commands, so just looked through it. I don’t see a call that says something nice like “play mp3 called bark.mp3” Instead it seems you would have to index a device yourself, and control the song skip though the interface. That is, if you had tracks 1.mp3 2.mp3 and 3.mp3 on the stick, your command sequence might go something like TURN ON, USE USB, SKIP, SKIP, PLAY to play 3.mp3. You did mention you didn’t want to do it, but putting a Pi or Beaglebone on your receiver would allow it to be used as an audio sync. I just don’t think our devices were created with that in mind. How far away is your receiver from your openHAB server? Run a cord?
There is a lot of work going on in the land of the Sonos to allow it to be used this way as well.
I need to come back and edit this post with some updates. I just spent some time reading through the docs and the source code for the Denon binding. It is actually more versatile than I initially thought. I was able to use it for my recently acquired Marantz as well as the older series. Additionally, the binding allows you to pass along a direct call to the AVR using the COMMAND tag. My initial sequence above was speculation, but I now think it could be made to happen.