Hi BEBOP,
Happy to pass on my experience. I have owned a 9000PRO for about 12 months now. Before buying it I had a good shop around even though at that time, I played a PSR640. My impression is that It's a great instrument and a great "all round performer". I chose it over the 9000 because of the 76 keys (vs 61 on the 9000) and amoungst other things, its great keyboard feel (totally different - for me, superior - to all the other PSR's). The build quality is very strong. The sounds and equipment level are great (apart from the great feel and the 76 keys), these were the deciding factors for me. I put in a 10GB internal hard disk, the detachable lights, a foot controller and volume peddle, and a shure WH20 headset microphone. I run it through a pair of powered (120W each) amps.
Over-all if I had to make the choice again I would still go for the 9000PRO. I am fairly critical of this sought of technollogy but have no complaints about the 9000PRO. It just delivers everytime I call on it (and that is everyday).
I hope this helps you.

Jon.