Hi Micco
Maybe you already know this:
YAMAHA has the most powerful MIDI standard. It's called XG.
PSR 9000 is XG compatible. Download XG Midi files, and you will hear the difference. Once you get into XG Midi authoring, GM sounds stale.
If you are just playing GM Midi files, you are not experiencing the real power of your PSR9000 MIDI playback.