The 8363Hz sample rate is what Scream Tracker expects. I'd assumed it was what the Ultimate Soundtracker expected too, due to what was easiest to play on the Amiga's Paula chip, but the only ST-XX disks I can find (archive.org's versions) have been converted to .wav, Wikipedia doesn't seem to mention it, and I don't have an Amiga, so I can't verify this. While sample rates don't really have anything to do with a pitched sound clip's fundamental harmonic (Nyquist-Shannon sampling theorem aside, as ~8kHz isn't going to be high enough to capture all the upper harmonics anyway, as evidenced by listening to such samples), 8372Hz is the fundamental harmonic of C-9 according to the Csound manual, appendix B, so it does indeed seem likely that someone's original thought was to use a sample rate that's a multiple of the note's harmonic, although why they did this, I have no idea. I can't think of an advantage to that. I guess it might theoretically make the in-tune sine waves slightly smoother?
Anyway, yes, you're right, I should allow the user to define an arbitrary sample frequency (and ideally bit resolution) to convert the files to, ideally with the whole 8-bit 8363Hz thing having a preset option like --tracker or something. I'll reserve the right to modify my script to allow this at some point, although it's not a high priority right now. It's open source though, so if anyone else would like to add any features, and they're useful and well coded, I'll be happy to merge them in.
Thanks for the advice!