Frank,
Where do I start?????? I had a PA80 for a very short time, and I still have a 9kpro in my studio at home, so I feel qualified to answer with little or no bias.

Sounds:
Yamaha has a much better grand piano sound
Korg has an edge in guitars.(slight)
Most orchestral solo sounds are about even - the Yamaha has two expansion slots for adding new samples and modeled sounds, and the on board sampler is not too shabby. (I'm told) The new Korg o/s is supposed to have some sampling options.

Styles:
Yamaha is more generic and smoother in transition. VERY useable in many song styles. The Korg drums are among the best I've heard, but the programmers were on a caffeine high when they recorded the fill ins and the variations. Too choppy and busy for the real world. Very cool patterns, but Steve Gadd on speed is the drummer. I want Ringo Starr - give me the beat Frank,

Buttons / layout:
Yamaha is SO FAR ahead here. The layout is soooooo easy. The multi pads and one-touch settings are in all the right places. The Korg engineers made this thing look nice, but the buttons are in all the wrong places for most players that use two hands to play the keyboard.

Size / weight / price:
All things considered - the PA80 is easier to tote around, although the Yamaha has a much better, solid keyboard feel. Korg is cheaper, and rightly so - it doesn't do as much, and is not expandable.

Mic / harmonizer:
This is where the Yamaha shines. In fact ALL the effects on the 9k are superb. The harmonizer works excellent from the chord section of the keyboard, or direct from midi files. the Korg harmonizer is very light on features, but the tone is good. There are no presets, no special edits available - the Yamaha blows it out of the vocal water here.
These two are really not a fair comparison - the 9k is a class above the PA80 in almost all areas. A better comparison is the PSR2k, which is a better value in most ways because of price and features. If you are a Triton fan, the PA80 will sound good to you, but if you are an avid fan of arranger functions, and need real time control over important features in a "live" setting ...... the Yamaha is the better choice.