Is it possible to see Roon as a server on a Yamaha Aventage Rex-a6a?
I’ve moved your question into the Audio Gear Talk category of the forum, because it’s not one that is dealt with by the support team directly.
Do you mean the Yamaha RX-A6A receiver? This is shown on the Roon Labs Partner page for Yamaha as Roon Tested.
It can certainly be connected as a Roon Zone, preferably via HDMI so that it will playback multichannel audio.
However, the RX-A6A will not “see Roon as a server”, rather it is Roon that will see the RX-A6A as an audio device to which it can send an audio stream to.