gnarlsnishi The only other difference I can see in hdmi0 nodes between Rock 5b (3588) and 5c (3588s) is something related to FRL support which is not (or should not be) linked to HDMI audio support. I've updated the rock5c image in my testing share so device-tree has the extra line though, but I can't see it changing anything. So:
a) Put Kodi in debug mode, update to the latest 5c image in my test-share, reboot, then run "pastekodi" and share the URL so I can see some other things in the system log.
b) If that didn't magically change something, edit extlinux.conf in the boot partition of the SD card and experiment with some other rk3588s board device-tree files (all are in the 'rockchip' folder on the SD card) and see what happens. Some might not boot. Some might not show HDMI either. If one does show HDMI audio .. let me know which one.
EDIT: Wait 30 mins until I rebuilt and sync'ed new files!
EDIT: Files are now posted..
Log here: https://paste.libreelec.tv/together-gnat.log
Possibly a relevant error at line 1792? In the mean time, will play around with some other device-tree files and report back.