The PSR-S900 has it's fingering modes, which include bass inversion, called "fingered on bass" in Yamaha speak, in a menu...it's no problem at all to get to it...even whilst playing.

The PA-500 looks like a great instrument...light and easy to transport, with some terrific features.

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