Yamaha's P85 digital piano is 25 lbs...it has an 88 key weighted, graded hammer action...AND it has speakers.
Casio's Previa PX500L has speakers, 88 weighted hammer action keys, AND arranger functions...it weighs only 27.5 lbs.
It should be possible for Korg to make a lighter 88 note arranger...perhaps they could make it without speakers...that would save some weight....but 51 lbs(without a road case, even) is far too heavy.
Ian
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Yamaha Tyros4, Yamaha MS-60S Powered Monitors(2), Yamaha CS-01, Yamaha TQ-5, Yamaha PSR-S775.