The limitation is caused by the fact that, once J River has handed the url to HQPlayer using my script, J River no longer knows about the URL, and there is no longer any syncing with the UPNP server. This can include Qobuz, Spotify, Tidal, or any other sources the UPNP server in question supports. If you are wiling to play DJ though, it can open up the possibility of sending tracks from any source which can be served from an appropriate UPNP server. There is no possibility at this time for playback of entire albums or playlists. This is because you are limited to sending just one track at a time. Don't get too excited though, because once more I have to add the word 'limited' to the title. Now I have added a small enhancement to this DIY script to support feeding JRiver and onto HQPlayer from UPNP servers.

Then it evolved into something which, I believe, is quite full featured. My solution for using JRiver as a front-end to HQPlayer described in this thread was described by me as 'limited'.

Jriver qobuz plugin