i’m not sure if this is even possible; tried it myself a long time ago and it didn’t work, most probably because of the mixed Airplay versions:
- aTV to HomePod pair is using Airplay 2 protocol
- Roon to aTV is using Airplay 1
If you enable the HomePods in Roon and group them together, you will be able to use them as a Roon endpoint & they will even be stereo with newest iOS version.
There is no official Remote app for Apple TV (at least not yet; hope Roon will consider it in the future). If you want to use your aTV as a remote display to see what’s playing & co, have a look at “TV: Remote” app - Apple TV Extension - Roon TV Remote