DTS-HD MA (or HR) is not supported due to lack of licensing. The hardware supports it; it's just not enabled in the firmware. Any DTS-HD tracks will only output their DTS 5.1 "core".
DTS don't offer a specific license for media streamers (try filling out their license application form: you can choose from AVR, BD player, games console or software).
DTS and WD's position seems to be that they cannot add DTS-HD support without a license.
Almost every other media player manufacturer on the market seems to have found a way around it. I haven't seen a good explanation for how anywhere yet, other than in some cases the manufacturers might have submitted a licence application for a BD player (device supports external BDROM and / or BD ISO files I guess?).
The WD players now support lossless multichannel PCM in up to 7.1, I believe, so you could convert your DTS-HD tracks to multichannel PCM without loss of quality and get it working that way (yes, that IS a lot of hassle).
Alternatively, look into buying another media player that can meet most of your needs. There doesn't seem to be anything short of an HTPC that can do everything for everyone (I've pretty much given up looking for now)..