Deaton: CONGRATULAIONS on your new 9000pro and welcome to the PSR club!

I don't have any personal experience with these boards, but you can find an excellent description (including model numbers) at Simon William's great SVP World website:
http://www.svpworld.com/9000proreview.htm

Scroll down till you reach the expansion board section.

To order, contact your local Yamaha dealer or call Yamaha USA, located in Southern California, at: (714)522-9011

Good luck. - Scott