Playing MKV file with DTS surround Sound

Playbar doesn't support dts, it's mildly surprising that you're getting any audio at all. The only 5.1 codec the Playbar can use is vanilla Dolby Digital (note, not DD+, DD-EX or TrueHD, just DD5.1). You'd need to convert the audio to DD.

Any converter program suggestions?

You could try Handbrake to transcode. But can I ask what are you using to play the files? Depending on how many files you have it might be easier to modify or try a different media player.

In my set up I have Kodi transcode the MKVs with DTS tracks to DD5.1 on the fly seamless with an RPi. This is a really flexible way to play basically any video file type you may have ripped to and still get sound out of the playbar, IME.

If you have an Xbox One, it is able to play MKV files natively and will do its own audio transcoding to Dolby Digital if necessary (the audio format setting is in the console's Audio and Display settings).

I personally use Plex though, which like Kodi (mentioned by Sonosssss) will do its own realtime transcoding if necessary to play the video on the device you're watching it on. I chose Plex because of the large number of devices supported for playing back both video and music files.

I usually just play them from my USB drive.

Just started using Plex for music. How is the quality for movies? Realtime transcoding sounds awesome and pretty sure my samsung has a plex app.

Will it give me actually surround sound or just play from the playbar?

And can some dumb down kodi and RPi for me? If that's a better option I would like to look into it.

I usually just play them from my USB drive.

Just started using Plex for music. How is the quality for movies? Realtime transcoding sounds awesome and pretty sure my samsung has a plex app.

Will it give me actually surround sound or just play from the playbar?

Since it's coming from a built-in app instead of an HDMI input, it should be 5.1 output assuming the audio track is 5.1. Just make sure that the audio output settings in the TV are set appropriately for Dolby Digital. Using the Plex app on your TV doesn't cause the Playbar to play audio directly from the Plex server.

Davvis to run Kodi on an RPi it is very easy : download the appropriate OpenELEC image (depending on your Pi image), burn to SD /micro SD, connect hdmi and boot. CEC pass-through woks with many remotes put of the box. There are settings for dd 5.1(disable dts, enable ac3/ac3 transcode. ) But before you need to confirm that your TV will pass the audio from hdmi to optical.

If you already have a server running plex I would start with it to be honest.