Hello,
I have been working on a media box for a few weeks. I decided to go with LibreELEC to support my KODI install. I also chose a DIY kit from SupTronic to support a 2.5 HDD for boot and media + a board to support 8,0 CH sound. The whole kit came together very nicely and I got my Raspberry Pi 3 to boot off the HDD and been working well. I have not been able to get HDMI sound to work in KODI. I can get the analog to work but HDMI sound is being a major pain.
I noted after the fact that the hardware had been tested on OpenELEC, OSMC and other media players. But not LibreELEC 
Has anyone put together a similar set? I have done a LOT of HDMI troubleshooting and config.txt settings with no luck. The site is not big on details and Raspberry Pi wiki is not up to date for the 8.0CH.
I will go back to OpenELEC or OSMC if forced but by all my research this OS was the best long term choice.
Thank you for your time. 