Wow! Good find!
I'll see if I can duplicate this result by installed some kind of time sync
in the virtualbox machine that I mentioned.
As far as controlling the volume remotely, I think you're right in thinking
that the tunnel isn't a remote control onto the remote sink, it's a
"virtual" sort
At the risk of jinxing myself, I think I figured this out. I enabled
time sync (using systemd-timesyncd) on both client PC and server RPI.
This github post[1] gave me the idea to check on time sync.
There is a hint about this in the Arch Wiki[2]: "Ensure that client
and server systems agree on
