The aim was to make it accurate to the original. To that end, the PSX music is the best way to go.
PSX sound emulation is miles ahead of where it was even just two years ago, so that's not really a bad thing.
Changing the music doesn't require any registry changes. Weird. Are you sure they've been making changes?
The Steam Database (I think Valve changed the name when I wasn't looking, it totally used to be called Steam Registry) is unrelated to the Windows registry. It's an internal database of absolutely every product, bundle, DLC, etc on Steam.
This page explains a bit more a bout how it works, but in short, it's often an easy way to see information on updates and sometimes even products that haven't been made public. It's also how I know they're working on a Steam version of
Final Fantasy VIII, even though they've never so much as mentioned it.