I know that Roon can recognize and control Sonos devices and stream music to them, but I would like to do the opposite. I would like to build an ultimate Sonos endpoint using Roon and higher quality gear but be able to stream to and control it from the Sonos app as if it were a native Sonos device.
Is that possible?
In a word NO
Roon normally supports RAAT connections and Sonos has no idea about this protocol.
Unfortunately not. Sonos devices can be enabled in Roon as zones. Sonos controllers (app, desktop) can only see Sonos hardware devices. If you have a Ropieee or RoonReady or other device that is not a Sonos device, then Sonos can’t see it. Sonos controllers have no idea what your Core is.
You can “take over” a Sonos device which is currently playing a Roon stream with the Sonos app to pause or change volume or replace the music. However, there are a couple idiosyncrasies - (1) you often have to do the action you want to do “twice”, because the first time you do it, the Core will think there was a network glitch and try to “take back” the zone and typically succeed, so (for instance) pausing a Roon stream using the Sonos app or a Sonos hardware button requires several taps, and (2) once you’ve changed the stream, your Core doesn’t realize that the zone is gone so it keeps merrily downloading from Qobuz/Tidal/Local, transcoding, etc so it will both “look like” the zone is still playing whatever it was playing within Roon, and your Core will still be doing all the work and/or consuming bandwidth. Once you understand this, it’s not too much of a pain - but good luck trying to explain it to anyone else in your family!
Apologies to the initial poster but I can’t resist mentioning that I, too, experience these issues when targeting Sonos devices and wish there was a solution. My HiFi setups aren’t Sonos but I’ve got a bunch of Sonos zones driving ceiling and outdoor speakers and, for those zones, I’ve got little Lutron audio controllers on pedestal stands for managing transport and volume. Pressing the play/pause button on those controllers when Roon is driving the zone always requires a second press and can, as @Johnny_Ooooops points out, leave the zone is a funky state. I wish there was a fix for this - seems addressable.