I was told by someone over at the AVSForums that the Panasonic DMP-BDT320 Blu-Ray player will decode 5.1 and 7.1 audio and output full quality multi-channel LPCM audio from the HDMI port. The Panasonic also has a usb port and will play back MKV files on an external hard drive or over the network and decode the audio.
For $145, I will probably pick one up and see how it works. It could be the answer to my search for a source for the Realiser that will play MKV files.
I have found that many Blu-Ray players will decode DTS, but they revert to lower bandwidth DTS even if the disk or file is DTS-HD. Also many will mix down to 2.0 channel for Dolby Digital files.
This LPCM via HDMI is really proving to be tougher than I thought. It's not a very commonly needed feature on AV receivers or media players. I guess I may have to end up going with the analog inputs as a backup.