Maybe the DTS HD Master or TrueHD tracks which are unsupported? Don't know if the Xbox playback software supports it. All others looks okay.
Don't unterstand why an HD audio track is needed to playback something on the Xbox. To hear the addional "HD" details, you must have 10K$+ equipment with 5/7 or more very good speakers.
MKV playback, recompression, remuxing, codec packs, players, howtos, etc.