Hi Victor,

I did play the Pa3X in one of the stores here. Its key feel is very good. Some of the sounds in the Pianos, Organs, Strings section really stand out. Korg states that it has twice the WAVEROM as the previous PA2X(PA800`s big brother).It has all the features you need. But sounds, again could be subjective.
In the following UK launch demos of the PA3X, it sounds fantastic, but I am sure its setup well :
UK launch Part1
UK launch Part2

If its mostly orchestral and ballad music that you play, then I second what Donny said about the Tyros. Its just perfect for such playing. Having said that, it won`t be a bad idea to wait for the Yamaha S910 replacement which is likely to happen sometime soon. It will be very close to the T3 specs but likely without aftertouch.

The Yamaha arrangers like your S900, to my ears, don`t need much tweaking excepting for boosting the Drums may be. It sounds good out of the box.To add to it, you could even couple it with the Roland Bk-7m module for more contemporary open sound for pop/rock genres.

All in all, I think thats a lot of keyboards in the stack along with what you already have And the upcoming Yammie + Roland Bk-7m + Korg Pa500 .. you won`t miss the BIG Three and without breaking the bank on a TOTL arranger

Good Luck !!