Heinrich. I can't fully answer your question, but as I have both PSR3000 & KORG PA50 I thought I would throw these comments in.
The 3K is an excellent board with a poor keybed, is about the best value Yamaha arranger.
The Korg PA50 is half the price and although does not contain sweet type voices the package is more professional providing on the fly adjustments like an assignable slider. Pads that are assignable. The keybed is far better quality than the 3K. You already have the Motif & Midjay, so the Korg PA50 would fit your needs with very little outlay.