MTC is an interesting one, but I gotta be the killjoy here:
The original files on NICHION are/were LAME VBR5. These are VBR files up to 150 kBit/s (and the typical 16 kHz cutoff), which sound decent enough, but you should not touch those files anymore because them being already weak on the audio data. While I am one of the few here absolutely fine and even a bit euphoric about lossy compression, the files you share are not only an upscale to 320 kBit/s, but also a transcode to AAC. Maybe that is the reason why the compression is so heavily notable: Letting the AAC encoder comb through it again you scrape off more of the already low audio information that the VBR5 MP3'ification left. And it's not that much..
As usual, I appreciate anything put up here and as you said, for illustrations these are fine, but I want to make this clear. I have a bunch of MTC from NICHION (the MP3s) and it's a great library, but also comparibly rare compared to, let's say, KPM.