I don't know why silver sounds better, but for IC's it does to my ears and it made me stop looking for anything else.
Still, there is a law of diminishing returns, and that you can only upgrade your Mazda so much. :) Meaning, it may be a great car for you but no amount of money will turn it into a Lotus or Bughatti.
So worth thinking about that before investing.
Also, of course, room acoustics. They will help get you off an upgrade cycle pretty quickly.