Beachy, if you can swing it at all, go for an S910 if at all possible.
The differences on paper may look subtle, but, believe me, the S910 is a big step above it.
Also, the S910 uses the newer style engine with the special guitar emulation.
If you really have your mind set on an S900, well, I wish you all the best in getting one at a great price.
Best of luck,
Ian
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Yamaha Tyros4, Yamaha MS-60S Powered Monitors(2), Yamaha CS-01, Yamaha TQ-5, Yamaha PSR-S775.