Panasonic UT50 Audio MKV USB Optical Out

This subject can get very technical so I'm going to try my best to explain it in a very simple way.
I have Serviio running across my network DLNA, plays all formats/audio/video great through TV speaker.
I copy my AVI/MKV files to USB and play them through TV USB port I get video, but audio is only static noise.
I plug in my optical out cable to my receiver and I get video, but audio is static noise.
I'm guessing that the TV is allowing audio decoding to pass through it's speakers, but the optical out will only play PCM/Dolby Digital, this must be true for the USB audio file decoding as well as they both behave similar with only static audio noise.
Question is why and can it be fixed?
I was hoping there was a way to take my MKV files and convert the audio to something that is compatible with my TV ie PCM/Dolby Digital? Or convert it from 5.1 to just Stereo..something like that.
I guess the best way to test would be to try different audio types until one works. Problem is I have a lot of MKV's I don't want to remake again.
Any help/Suggestions...hope this makes sense.
Also the reason I ask this here in the Serviio Forum is because others have manipulated their profiles in such a way that it forced the audio to play only PCM on certain file types like MKV.
I have Serviio running across my network DLNA, plays all formats/audio/video great through TV speaker.
I copy my AVI/MKV files to USB and play them through TV USB port I get video, but audio is only static noise.
I plug in my optical out cable to my receiver and I get video, but audio is static noise.
I'm guessing that the TV is allowing audio decoding to pass through it's speakers, but the optical out will only play PCM/Dolby Digital, this must be true for the USB audio file decoding as well as they both behave similar with only static audio noise.
Question is why and can it be fixed?
I was hoping there was a way to take my MKV files and convert the audio to something that is compatible with my TV ie PCM/Dolby Digital? Or convert it from 5.1 to just Stereo..something like that.
I guess the best way to test would be to try different audio types until one works. Problem is I have a lot of MKV's I don't want to remake again.
Any help/Suggestions...hope this makes sense.
Also the reason I ask this here in the Serviio Forum is because others have manipulated their profiles in such a way that it forced the audio to play only PCM on certain file types like MKV.