As a Tyros 4 owner, here are a few things about the Pa3x that appeal to me:

1) Korg Songbook feature
2) TC Helicon Voice Live 2 Technolgy (supporting rootless chord recogntion)
2) Chord Sequencer
3) Shorter overall keyboard length
4) Punchy more agressive sound for a raw rock-club sound
5) Physical Sliders
6) Covenient to snap on/off speaker monitors

One major feature limitation concern is Pa3x's support for only 2 footswitches. I require a minimum of three: sustain, fill, and vocal harmony on/off.

Soundwise, I haven't yet heard any new instrument voices or styles dramaticalky different or improved over Pa2x so hope to hear demos from Korg to showcase them. That said, as a happy satisfied Tyros 4 owner, I still can appreciate owning a Korg Pa3x too, for its punchy live sound and advanced features.