When I was using my pS3 as a media box, I would host the MKV files on my main PC. To play them on a PS3, they need to either be transcoded or remuxed. Using a streaming app like PS3 Media Server or TVersity, the files are transcoded - they re-encode the video and audio into a format that the PS3 can recognize.
The alternative, and what I did, is to remux the files - only change the file format to one that the PS3 can recognize. The video and audio are untouched, and remain full quality.
To do this, simply convert it with
this program. It only takes a few minutes, and once it's done you have an MPG file that can be streamed with any DLNA program like TVersity or whatever (I just used Windows Media).
So if you want a dedicated host box, you could convert the file first, then send it over to it, or control it via remote desktop and do it that way. This does add an extra manual step though.