Make sure you mux the file with MKVMerge v4.0 or earlier, because later versions enable a function called “HEADER REMOVAL,” which the WDTV does not currently support.
If Header Removal is turned ON, you will get NO AUDIO at all.
You can confirm this by using the freeware tool “MKVInfo” as part of the MKVToolnix package.
If the MKVInfo lists a compression type, as demonstrated here:
| + Default duration: 32.000ms (31.250 fps for a video track)
| + Audio track
| + Sampling frequency: 48000
| + Channels: 6
| + Content encodings
| + Content encoding
| + Content compression
| + Algorithm: 3 (header removal) <----- HERE
| + Settings: length 2, data: 0x0b 0x77
then that file will not work on the WDTV.
By the way, DTS-HD and DTS-MA are the same thing. DTS is more correctly known as “DTS-HD Master Audio.”