Okay, so the Quenc trick works with DTS-HD. Yey! One Blu-ray to DVD conversion down!
Now, I'm trying my Dark Knight Blu-ray. Several problems so far.
1) When extracting the main AC3 source, FFMPEG gets 88.06 seconds into the audio track, and then just sits there, eating CPU cycles.
2) When I attempt to extract the main TRUEHD track, I get the following error:
http://mirror.adubvideo.net/truehderror.png
I'm updating my FFDShow build (fixes an error with ffmpeg-mt) and then I'll try using AC3 loaded directly (no demux). I expect that this will work just fine.