If you want some S98 files to play with, I've uploaded my whole collection (~215 sets, 60 MB) here: http://www.sendspace.com/file/282nuv
First of all, there should be a selectable FM to SSG volume ratio. PC-98 did allow changing that with a BIOS setting AFAIR, and some games were made with special values in mind.
Values I see used most in Hoot are fm_mix=0, ssg_mix=-18. AO is pretty close, but I think the SSG is a bit too loud.
Second of all, no S98V3 support, meaning about half of the available sets won't even load (everything using chips other than OPN/OPNA is no good). Here's more info on the format:
Thirdly, S98 files using OPN/OPNA should be rendered in 55466 Hz, those that use OPM in 62400 Hz. Those are native chip frequencies, not using them results in some aliasing artifacts.
The Girl Who Sings Love at The End of This World Yu-No (1996)(Elf).rar\yuno043.s98www.snesmusic.org/hoot/yuno43_hoot.oggwww.snesmusic.org/hoot/yuno43_ao.ogg
Furthermore, something's seriously fucked up with OPNA sets that use Rhythm channel.
Chatty OPNA (1988)(System Sacom).rar\02_Opening1.s98www.snesmusic.org/hoot/chatty02_hoot.oggwww.snesmusic.org/hoot/chatty02_ao.ogg