Thanks kszaq - I bought the S905 on the basis of previous posts which said it supported PCM audio in excess of 96kHz which seems to be the limit on the S905X. It's odd that I can configure Kodi to send 8 channels of audio at 192kHz ok, but the PAplayer (and videoplayer) both seem to fail at setting 2 channel audio at 192kHz. I assumed it was an issue with ALSA, but it may well be a problem with the driver as you say. Is there a forum or link you could recommend where I could follow this up?
I dealt directly with some of the developers on the Kodi forum and supplied sample files several years ago when they were developing the audio engine for linux. My ION2 board player works perfectly at all audio resolutions with LibreELEC, but it doesn't have any 4k video capability which is why I went down the AMlogic route. So near and yet so far!
sound/soc/aml/m8: work-in-progress by Kwiboo · Pull Request #23 · LibreELEC/linux-amlogic · GitHub
I again took a look at 10bit output and stumbled across this commit:
Unfortunately /sys/class/amhdmitx/amhdmitx0/colordepth does not exist and I cannot create it:
This commit is not for S905/S905X/S912, it's for other TV SoC.