I had only tested PCM so far. But all PCM bitrates were fine up to 192kHz - but only in stereo, no multichannel. Interestingly, my SACD ISO test file with 2.0 and 5.1 layers had the track list displayed with each track appearing twice in the list - the stereo and multichannel version. Each track played back as 2.0 though. The same ISO played in Kodi 18 on CoreELEC just plays back as noise, so the SACD ISO filesystem support is much improved even if the PCM audio has not quite caught up yet. I'll test passthrough audio on my DD and DTS test files later.
EDIT - passthrough audio in general plays ok, I tested DD+, DD TruHD, DTS-MA channel test videos and all were ok in audio, but video playback varied from working ok to blank screen or picture tearing or sparklies. None of my DVD ISO files worked (just displayed as folders with Video_TS files), but I think this is a known kodi 19 issue.