CatBus said:

Okay, this is plain weird. I'm trying to make this BD-compliant, and so I re-encoded the video (works fine), and the main audio also works fine without alterations, but I'm having a heck of a time with the isolated score and French tracks. I've tried re-encoding and everything--they're just dead silent on my system, but play fine on my PC. Any ideas? 48k sampling, 16-bit audio, not much that can go wrong there, right? Weird watermark/copy protection issue? No idea.

No copy protection issues. Processing-wise, all audio tracks were completed the same way, so they should all work the same way.

You should not need to reencode the video. It is already in h264 format. You would just need to change the container from MKV.