So close but no luck (i.e. sound) yet

[Tigo72]

I love the idea, but I just can't get any player to actually play music. The page on port 32488 shows up, linking works, just as confirming the link (already linked). Plex sees the players, I can connect or so it seems --- but then, nothing happens. I keep seeing the famous little spinning wheel spsinning forever, but no player will really connect and play music or even be controlled.

I've fiddled with every possible firewall setting on my Synology (from where I run the docker). I am on the host-network, tried every multicast setting in my router on or off, snooping etc etc. I feel I am very close, but it just won't happen. Perhaps anyone here has a brigth idea? I would really appreciate it.

Thanks, Tigo