[RPi5] Multichannel FLAC

I have a rPI5 with LibreElec 12.0.2 connected to a AudioLab 8000AP via HDMI. The latest firmware is installed on the rPI5

I'm trying to play multichannel FLAC files with no success. I have
- Pass through disabled
- Audio Output configured to vc4-hdmi-1, MAI PCM i2s-hifi-0 with 5.1 channels and I've tried:
fixed - Processor sees 5.1 PCM when playing a 2 channel file
optimized - Processor sees 2.0 PCM when playing a 2 channel file
best match - Processor sees 2.0 PCM when playing a 2 channel file

I know that the HDMI input can properly accept 6 channel PCM as my Bluray player, a Panasonic UB820 can successfully output 5.1 PCM into the processor.

However when I try to play a multichannel FLAC such as the tests from https://github.com/sfiera/flac-test-files I get broken output from the multichannel files. The 2.0 file is fine but for all of the others the processor initially gets sync and lights up with 6 channel PCM on the display but then reliably moves to showing silence half way through the the centre channel being played just after the word 'Front'. I've tried both the audio player and the video player to play the files.

Does anyone know what is wrong here or how to go about debugging for fixing it?

Slight clarification I'm using the latest firmware available via LibreElec which is 2024-11-12 not the latest that exists.

And one more update I managed to find a 5.1 WAV test file which plays successfully with the correct channels to the correct speakers thus it must be the FLAC playback itself which is the problem rather than the rest of the system.

To conclude this I took the Fraunhofer IIS 7.1 test track, these are usually provided in AAC but I converted to LPCM to test. This plays back correctly. I then converted that LPCM to FLAC using xld and that also plays back correctly on LibreElec 12.0.2 / kodi 21.2

The FLACs from the github repo playback correctly using macOS's built in support, which does something funky with virtual surround with the multichannel files. However from my testing do not playback correctly on LibreElec 12.0.2 / kodi 21.2. However from your testing mostly play back correct on LE13 nightlies however I'd rather not update my setup to a nightly to test this.

My aim is to play 5.1 FLACs of a variety of choral music which was originally released on SACD but Audite have now released as multichannel FLAC which can be bought from their website.

I guess even if the bought FLAC ends up not playing correctly I can convert it to LPCM and that should work.