The Tyros3 allows you to layer three voices in the right hand, the S910 can layer two.

For my style of playing, it made no difference to me, but it might to you.

The S910 does not have a hard drive, but uses an external flashdrive instead, which I also prefer....no moving parts.

Ian
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Yamaha Tyros4, Yamaha MS-60S Powered Monitors(2), Yamaha CS-01, Yamaha TQ-5, Yamaha PSR-S775.