So I've figured out HD audio passthrough issue. Turns out it was dumb user error. There is a setting which specifically disables it - "Sync Playback to display" - btw: this is
not related to change TV refresh rate to match movie (aimed to smooth video)
https://forum.kodi.tv/showthread.php?tid=307165
Official Plex Kodi plugin is now free. Yes - it's looking pretty and matches well to regular Plex web interface, but tbh it's not really well optimized to run on limited hardware where GPU is aimed to do heavy lifting on anything graphical.
Probably going to try other Plex Plugins. I used both unofficial ones before, probably would go back to trusty PleXBMC.
TL.DR.: Official Plex Plugin for Kodi has slow gui on Khadas VIM box, but otherwise Kodi GUI itself is very fast.
@sholling I had played a bit with DroidPlex a bit and I might eventually switch to using it full for full remote and 1gig network, but now it's very close call. For now it would stay plan b) or second room device.
One thing to say 'about community based LibreElec build for my KV box is it auto-updates it's LE version on boot and it's absolutely seamless which is nice to have.
Not quite the case with more proprietary dual-boot Droidbox. I could probably re-write the internal storage to install regular LibreElec without dual boot, but I am guessing that some devices like BT, IR and Network may or may not work correctly. LE version shipped on Droid box is a bit behind, not much. It has Kodi 17.5 where is the latest Kodi is 17.6 which was released mid november '17.
I've finally managed to make the $50 box work as very good HTPC, but it took decent amount of IT work, reading and re-reading guides on forums. Fixing up some mistakes which I've done (like full internal storage reset - shouldn't have done that) Figuring out how EXACTLY build a custom bootable SD card for my specific device, which luckily it's could be considered it IS somewhat supported thanks to efforts of dev goes by forum name
kszaq