www.makemkv.com

I recently purchased a Sony A9G OLED and it's amazing. The issue I'm running into though is that when I try playing a UHD MKV version of a movie, it just doesn't have quite the same brights and dark's as the disc version. I've tried playing through Plex (it's direct playing) as well as Kodi but it's the same (everything is always played through a Xbox One X). Either way, the 4K discs just seem to have more color range than the digital copies do. My roommate notices the difference as well so I'm not going crazy.

Any idea what the issue could be?

First post here. Thanks for your help!

Is the movie in question a "Dolby Vision" disk?

If so, you'll want to read through the rather long and convoluted topic Dolby Vision now possible through MP4 Mux.

It is not, just standard HDR10.

Thanks for your input!

There is a possibility you need to learn to configure and/or start using a proper renderer if you are not using one already since it sounds like you are playing these off a PC.

Example:

http://madvr.com/

That is one of the best (if not the best at this time) for PC playback of UHD content. There is a link to their own support forum in that main page as well. Plus plenty of how-to-guides available and easily found through a simple and quick Google search.

It sounds like you are creating your MKV file without HDR or your playback software/hardware does not support HDR.