I had a problem getting audio to work on the HDMI port. First of all I manually checked all the following:

• Unmute the S/PDIF output using alsamixer.
• Opened the XFCE mixer app pavucontrol:
  • Into the Output Devices tab check that the HDMI #1 is unmuted and Set as fallback.
  • : Check the the pavucontrol uses the correct master volume…
  • Start an audio player (e.g. the audacious program to play some mp3 files), into the Playback tab check that the app is using the HDMI #1 port to route the sound.

Now you should ear the sound coming from the HDMI display (abviously your device must have the speakers!).