Hi seanbaker,
I tried to go to your web-site, no luck, is it down? Here is a link to the "Motif" web-page at "Yamaha" :> http://www.yamaha.com/cgi-win/webcgi.exe/DsplyModel/?gSYS00005MOTIF
It reminded me of a couple of go pionts, the appregeator (multi-poly-?) means that you can play multiple notes at the same time [ie: C cord=C-E-G in harmony with an Em cord= E-G-B and have them interact with eachother ( I think ) Also you could have a "piano ref`" and a "guitar strum" at the same time ( if it does what I think ) I say that because all appregiators are not the same ( I think you can down-load the "Yamaha-Motif" manual) and the other point is it has a USB out-put for either "Windows or Mac"
As far as learning a new KB for me anyway it has always been a "hands on-learn by doing" so I think no matter what you decide I don`t think it would be to hard (might be fun) You can also download the 9000Pro manual at "Yamaha`s" web site as well .
You`ll get there--- Keep in touch-- best of luck, I hope I have helped !
jedi