I am also a user of roon and love it. If you are going in the upnp direction you would probably need to look at software like volumio, emby, plex, tversity and the like to act as upnp servers. You would then need a upnp client/control point like mpd to control the server. I don’t think any of these are free anymore. Bubblepnp (I think) is free and could get you part of the way there. So you need server software, roon or otherwise and you need a client of some kind to control the server and direct the audio output to an end point of some kind. Hope that helps.