Multichannel FLAC on rPI5 with LibreELEC

    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?

    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.