Samsung UE40ES6710 cannot stream subtitles and view .mkv

Hello.
Currently I'm using macbook air with external USB hard drive to stream videos to my Samsung UE40ES6710.
For some reason I cannot stream subtitles with it. The subtitle file is in the same folder with the movie file. Both files have the same name.
I tried to force it by setting up " always enable burned-in subtitles, no joy.
Any idea what am I doing wrong? any advice?

Additionally my Samsung tv does not recognise some of the .mkv files
Like a russian roulette, you newer know what is going to work or not. The same files, streamed via Kodi, are working just perfectly fine (but again, without subtitles)

[atc98092]

Can't speak to the subtitle issue, but for the non-playable files, you must remember that MKV is simply an container, and what matters is what is in that container.

There is a wide variety of video and audio codecs possible in the MKV container, depending on the source video. If it's a DVD rip, it is likely MPEG2 video and AC3 or DTS audio. A Blu-Ray rip could have AVC or H.264 video, and a wide variety of audio possibilities. We would need more information about the files that play and the ones that don't. If you are familiar with MediaInfo, that's the easiest way to get the file information. You can also use a FFMPEG command line to extract the info.

I'm not familiar with that series of Samsung, so can't speak to what will and won't play. My H and JU series can play almost everything, but they're newer than yours.