George,

I agree, the grand piano sound on the PA1X pro is not bad at all. It is just like any other synth, very acceptable sound in the mix but not like a real piano sound that can be played solo.

It's just a matter of taste I guess, I kind of prefer the piano sounds of Motif and Roland XV slightly better than PA.

I for one am not buying the piano board for PA. Keep in mind, almost all major companies, including Roland and Yamaha offer Piano expansion cards for their synths. Korg is not the only company doing that.