OK I have the TV to myself today.
I discovered a bug.
I removed the Justboom HAT and config code to temporarily remove any unknowns.
I used HDMI from the with SPDIF passthrough from my TV set to Optical out. So the TV plays back in 5.1 channels to the AMP from both TV direct first and then through KODI.
I tested this with my sample DOLBY ATMOS and DTM files. These all played perfectly. I noted that all of these samples are H264 DOLBY or DTM 5.1 channel codec videos.
When I play H265 encoded files they play in 2 channels only. I checked again with a non demo H264 encoded Dolby Video and 5.1 channels worked perfectly.
So I suspect there is a bug in that H265 encoded videos are no longer able to decode polyphonic audio. I will re-code one of the H254 DOLBY demo files to x265 and confirm KODI is no longer decoding this properly.
chook
My theory doesn't hold true. I converted "THX Deep note Genesis4k.mkv" which never displayed BTW, to HEVC-265 and resized it to 1920x1080. It plays fine. So I'm back to square, one. I try re-coding some of the x265 videos to 265again. See what happens.