[mrfeh]

My setup:  kodi 18.7 (RPi 4) -> hdmi -> amp -> tv

My speaker setup is 5.1. When the amp is being used for audio, all works fine. 

When I turn the amp off (want to use the TV's speakers), I only hear 2 audio channels (either front right and left or rear right and left). The center channel is gone, so if the source material is using multi-channel audio, I have no dialog.

Ideas? Thanks!

[alfton]

TV does not handle 5.1 set down to 2.0 channal on kodi when you want to use TV. 
OR se if you have sett some bad setting on sound on the television, TV try to do magic with 2 speakers, and that usaully is really bad idea.