I'm currently working on a full restoration of classic music.
The client used for P99 is missing some instruments from its soundfont, because back when sound cards were still a thing, they came with their own instrument banks built in.
Since we don't use sound cards today, this causes the music to come across choppy, and sound like it's missing some things. It's a relatively simple client-side fix however, and here's a video of some before and after comparisons so you can hear the difference for yourselves:
https://www.youtube.com/watch?v=I__3xM0aSyA
As the next part of the overhaul, I'm working on adjusting the sound emitters so that the music actually plays when and where it should, instead of cutting in and out unpredictably.
Once complete, I intend to release the changes as a a standalone modification at a bare minimum, depending on whether or not there's enough interest to make these part of the core classic changes.