The vast majority of lossless Atmos demos from https://thedigitaltheater.com/dolby-trailers/ are in the mkv format. 
I have no luck in getting my UBP-x700 player to play these from my hdd. I can play mkv separately , I can play Atmos separately, but not combined from a single mkv file. 

It’s been over a year since a firmware update was released, so I guess we won’t be getting any more. 
Has anyone got any help on this subject