My experience so far...
Equipment and Software:
Integra DTC-9.8 Processor
Radeon 5750 with 9.12 drivers (not the hotfix)
Playback: Windows 7, 7MC with MediaBrowser, WMF disabled, Gabest splitter, audio using FFDShow tryouts 3164, using Windows Video Decoder
MKV movies with 1080p and TrueHD or DTS-MA audio
M2TS movies with 1080p and TrueHD or DTS-MA audio
During boot up, I get "an incompatible signal has been received" error and no video, but this goes away after Windows boots up and the ATI driver is loaded. This means I can't access my HTPC's BIOS should I need to. Also, the HDMI sync is sporadic, sometimes I have to switch to another source and switch back for my Integra processor to sync and display video.
In 7MC, I can get MKVs with TrueHD or DTS-MA to bitstream to my processor. But for some movies (e.g. Into The Wild), the TrueHD audio is choppy and drops out every 4-5 seconds. I have no such problems with DTS-MA.
M2TS files with VC-1 video is choppy. M2TS files with AVC are fine. Bitstreaming HD audio works in either case, but is choppy along with the video.
No fast forward or rewind capability in MKV or M2TS. But I can skip ahead and back.
Any advice is appreciated. Thanks.