Today I found YOU and have installed CoreELEC on my MinixNeoU9H and also on Ugoos AM6 2GB.
Everything works perfect with Kodi on booth devices. Passtrough audio on Yamaha RX-V681.
Great 4K picture on my Panasonic TV. Great work CoreELEC.
Is it possible to install CoreELEC as a main and only system on my boxes?
Ugoos has now some Dualboot solution with OTG update. I must admit that missing OTG cable is reason that I dint been able to try. 
Best Regards
Ivan