Don't want to flame you but errr.... if you want to tweak songs, styles and sounds...
Have you ever looked into a Generalmusic keyboard? For instance a WK8SE?
I am sure you've got your reasons for having Yamaha, but the page comes to like:
A)"Hey guys, look what you can do with the sounds on the PSR9000!!! Amazing"
B)"ehm.... The GEM WK4 had it in 1996.... sorry!"
CU!
Joost