1. SSH into the sender using pi@sender-room.lindisfarne.nsw.edu.au (password in 1Password - PiControl Default)
  2. Go to /lib/systemd/system
  3. Edit files pa.listener.X.service and adjust the volume flag on the line "ExecStart=/usr/bin/omxplayer rtp://239.10.1.0:4444 --timeout 2 --vol -1000 -o hdmi". Value from -6000 to 0, 0 being the loudest.
  4. Save each file after the change.
  5. Run command line "systemctl daemon-reload"