As I suspected, all the music files that SLADE cannot identify are WMA. (That would be D_BLUE, D_EVIL, D_FROZEN, D_REFINY, D_SECRET, and D_VOLCAN.) For reasons that should be obvious, these will only work on Windows. Yes, a custom loader could be written for Linux that interfaces with ffmpeg to decode it, but considering you can just use something like Vorbis (with probably better results at the same 33 kbps), what's the point?
The irony that these are all WMA is that aside from D_BLUE, they all sound like renders of other formats that ZDoom supports natively.