Hello Friends,
i have turned around these problems for years. The last weeks i took a new approach to find out what the problem is with the HD Audio Formats not played back via passthrough because i upgraded my system to 4k playback:
My Hardware: NUC11TNHi5, Denon AVR-X3600H
First things first: Intel Nucs DO Playback HD Audio (DTS HD-MA, TrueHD, etc), it is not a hardware issue, like indicated above!
The Problem (after my research) is the pipewire and pulseaudio audio Server. They are occupying the ALSA system in such a way, that i cannot get HD Playback as long as the two are running.
I tested this today with a vanilla minimal xubuntu where i removed pulseaudio AND pipewire and OLA - it plays back! 
Until now i played back only with mpv media player. But now i want to try this way with kodi...
So here is my question: How do i remove or deactivate permanently pipewire and pulseaudio on LibreElec?
Any ideas?
PS: I reactivate this topic, because it is still current instead of starting a new thread. But the aim is to work out a detailed how-to to get this to work...