I have played both in the store. The live! grand piano sound on the Yamaha is far superior.IMO. there are 4 or 5 outstanding electric piano sounds, too. all far superior to the Casio.
the Casio has big edge in the organs and features. the lack of l/r outputs on Yamaha is big drawback to me..you lose the internal speakers when you have to use the headphone jack out to external amp. but Casio still refusesto have tap tempo button..to me essential for feeling a groove and going right into it.

Make the decision on your needs..both are incredible kb's for the $$$

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Miami Mo