Well, apparently, all Korg needed to do was put speakers and a TC harmonizer in the unit and they got me!
I've had the PA900 on the stand for about an hour and I'm trying to get to it as much as I can, but we're also trying to entertain 8 1st graders at a pool party in what looks like a crappy, rainy dy! Grrrrrr .... Sigh.

First impressions:
key feel - excellent
look - a tad cluttered, but easy to adjust to (the 3x is just so perfectly laid out)
speakers - not as powerful (at least so far) as the Yamaha, but I think with EQ and balancing it may improve. Seems quiet at first
tones: AWESOME
features: almost nothing is missing - the 3x sliders are easy enough to use in the touch screen, great C/S, lyric display, CD-G file readout etc
screen: seems easier and more responsive with less pressure than the 3x - like it
size/weight - BEAUTIFUL - sleek, attractive (still wish it was black, but the silver is cool)
mic - it's not the crystal clear high end sound that the 3x has, but that may just be the speakers settings (comp, eq, etc) ... I'll hook up to PA later today

Overall - I think it's a winner. The basic design is very familiar, and it will go on it's maiden voyage to the Jersey Shore this Monday. I'll have LOTS to tell on Wednesday when I return!

Stay tuned ..........