Tested with a 5.1 TV Show and:
If Kodi is configured 5.1 I barely can hear the voice of the characters of the TV show.. Just when I set it 4.1 works (But I'm sure there is one channel missing)
Also tested the Home Theatre just by itself (libreelec not running) with the sound test and all the speakers/channels are working.
What might be wrong?
Try downloading some dts or dd test filmes from Kodi websites. Check with sources which have proven multichannel tracks.