Unless you tell Kodi that a receiver supports DTS/AC3 etc. it will resample content to multichannel PCM with the number of channels determined by the default Kodi channel config which is 2.0 (stereo). If you enable DTS/AC3 pass-through, it will do it.
Passthrough works only when I play videofiles, but not with Live-Tv. Maybe there is a bugfix in Beta 1. VideoPlayer: passthrough fixes by FernetMenta · Pull Request #10247 · xbmc/xbmc · GitHub
I will wait in try again. Thanks for your effort!