I love using my Roku and Plex to play my movies back. It's nice to say "GET THE DISC!" - It's very common to say. I don't disagree that playing things off a disc is really the best choice. But, I still have 30TB of storage with thousands of TV shows and movies that I can play back with just a few clicks of the remote. This is a way easier method of accessing my collection. It's really awesome.
So, if your end goal is to get the best quality sound, then you need a playback device which supports this, and that would be Plex though the nVidia Shield.
Roku supports Plex and delivers audio, but it's a bit tough to track down exactly what surround formats it supports.
Roku also has an integrated player which you may want to try out for file playback which may work better for some things.
I wouldn't get hung up, at all, on trying to get your TV to do things that the manufacturer doesn't give a darn about supporting you on. They make TVs with a quality image. That's all a TV really must do. After that, go to other devices to get the best possible image to the TV and the best possible sound to the room.
At $100 for the Ultra model, it's a bargain that you'll be very happy with for years to come.