Since the Mvix Ultio does not decode Dolby Digital Plus audio streams in MKV files even thought all the paper work from Mvix says it does. When trying to play these files with DD+ audio you will get an error saying that the data rate is too slow. he video will play but not audio is heard. Here's the link that shows all the video formats the Ultio accepts and what type of audio is acceptable with each video format (http://www.mvixusa.com/download/manuals/mvixultio/Mvix%20Ultio%20Media%20Player%20Format%20Support.pdf)
Here's the solution that i've found to work.
1.demuxed the MKV with tsmuxer
2. convert E-AC3 audio stream to plain AC3 with eac3to_more_gui, i set the audio to 640
3. remux back to either an MKV or M2TS file with tsmuxer

**because i created my own MKV files and used the best audio i could from the source it may be that it is just MY files that arent working.** If this is the case please let me know if you are having the same issues with
Dolby Digital plus (E-ac3) audio not working in your MKV or M2TS rips.
thanks for listening :)

Yes, I have a same problem, DTS HD-MA is not working, ripped Blu-ray disk to m2ts, then just came out dts down mix, not HD Audio. I did contacted Mvix support, still waiting for the answer.

MKV files with DTS audio aren't working with 1.3 or 2.1 firmware.

MKV files with DTS audio aren't working with 1.3 or 2.1 firmware.

Mine didnt either I changed the sound to Raw and they played fine.

However I do not have any sound for my avi files.

Plays everything else fine but no sound for 1/2 of my collection