My Sony BDP-S3100 is a real nice player, but it's freezing up when I try to play MKV files with DTS-HD MA audio tracks. I looked briefly online, and it appears to be a known issue with Sony players. Dang. I was really looking forward to some glorious 7.1 audio. I can stream it from PS3 Media Server, but navigation is easier if I have the files on a USB connected to the Sony.
My HomeWorX HW-150PVR can also play MKV files, but I haven't figured out how to play 7.1 from it (if it's even possible).