tino1,
Yes, you can use the YAMAHA as a Midi controller to control the Midijay. You do not need to split the Yamaha - simply assign a SPLIT point on the Midijay and then use the left for chords/style/arranger and right for voices ... just as on any other arranger.
UD - not sure I can do any trades at this time. I also have some PSR 3000's that came in on trades towards the S900s ... got to move these guys first. However, I'll get you an incredible deal/price on the Midijay (unopened) if you like. Contact me at axa130@hotmail.com