Serviio is a nice piece of software and I would like to add my contribution to it's further development. I have installed on my computer version 0.6.2 and a Panasonic VT30 TV (best TVs in the world). Since I installed it I tested different MKV files and different profiles - Generic and Panasonic.
As you probably know, if the Generic profile is selected and the MKV file you are trying to play on the TV is supported by Panasonic, then you can play also the subtitle.
If you select Panasonic profile, then you can play almost all MKV files but no subtitle.
So...I looked at th properties of different MKV files, using MediaInfo (comes with K-Lite codec pack) and I saw that the only difference was that the files that won't play on my Panasonic TV using the Generic profile are different from the ones that are OK with only one property - they have: Muxing Mode: Header Stripping.
I tried to find a way to get rid of the Muxing Mode: Header Stripping and I found MKVToolnix (it can be downloaded from http://www.videohelp.com/tools/MKVtoolnix)
You have to select Disable header removal compression for audio and video tracks by default and Start Muxing.
It takes only a couple of minutes, because all it does is to copy the MKV file and doing minor changes.
I tried this process with several MKV files and it worked.
Remember to select Generic Profile so you can play also the subtitle files.
Hope it will help you.
I'm very curios if this "trick" will work also on other Panasonic DLNA enabled series.