I confess that I was attracted especially by the PA-2X pro, because I thought that it could offer an interesting option as a master keyboard.
It really has some deep features: the sampled loops/time slicing feature basically means that you can record or import a sampled loop -even stereo- sync it to a style or assign it to a multipad and then it will play correctly, no matter the tempo of the style. This is concept which has been implemented only by Ketron, with the big difference that their sampled loops (called grooves) are mono and, of course, Ketron arrangers lack the multipads.
Another interesting feature of the PA-2X pro is the ability to assign every part of a style to an internal sound or an external module/keyboard; this means that, for example, for a given style you could play the PA-2 own internal drums and then assign the bass to a Motif ES rack, the guitar to a Fantom XR, the piano to a Kurzweil, etc.
Finally, you can use it as a master keyboard, because for each channel of the right hand (R1, R2 and R3) it can send bank and program changes to external sound sources, and these settings can be saved within a registration, or whatever Korg calls them. This is something that no other arranger keyboard is able to do.
Add to this the internal sampler and the quick loading time of the samples themselves (at least compared with the Tyros 2) and you get a picture that makes you think.
Too bad for the fill issue and also the relative lack of support (Korg styles are even more difficult to find than Roland's...)
Anyway, I think that for now I will just wait and see...here is also the Midjay Plus coming out this month...