Danny,
I think Manuel's post is pretty much right on. When the PA1XPRO came out, many customers thought it was just a PA80 with a new face! After playing, everyone I know agrees it is much better board. Even though many of the original styles are included from the PA80, they have been re-worked with the better sounds. The "mega" type sounds are also very noticable in sounds like Trumpet, Trombone, etc. where they use multi layer samples to create the realistic nuances of a Trumpet player using lip, pressure, etc. to create a more natural sound.
You also get USB for easier data transfers from Computer to keyboard.
I just loaded version 3.05 software from Korg yesterday which added about 30 new features. Korg has done a great job constantly updating this keyboard to add everything customers are asking for.
By the way Scott Yee, they just added something they call "expert chord recognition" which I haven't tried yet but it might be your rootless chord recognition!
George Kaye
Kaye's Music Scene
Reseda, California