I have an S905X box (Nexbox A95X clone) lying around so I decided to test it with latest LE firmware. I used "LibreELEC-AMLGX.aarch64-12.0.2-box.img.gz" on an SD card with 'gxl_905x_p212_.dtb'. Here is what I found:
-When I tried to specify HDMI audio pass-through options, the DTS-HD MA was not greyed out. However when I played a Blu-ray rip with DTS-HD MA or Dolby-TruHD, I got only silence. So non of high-resolution audio format worked with GXL-212 board. I guess LE 11.x would be same. I did not test pass-through of Dolby-TruHD on S912 box.
-I tried to play a Blu-ray rip (1080p with HD audio) with DRM PRIME decoder' option turned on, I sometime got flashes and blobs of color and HEVC seek froze the playback.
-I tried to play a Blu-ray rip (1080p with HD audio) with DRM PRIME decoder' option turned off. It worked with 5.1 audio but you are right HEVC seek broke the play back.
- I did not even bother with any 4k video on S905 box.