Depending on what's available in Spain, I would recommend the Roland Juno D...more polyphony than the Yamaha MM6, which would be my second recommendation.

I haven't tried the Korg X50 or the Roland SH-201 so I can't comment on them.

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