Hello Fran,
A few years ago, I needed an Expression Pedal for one of the many Technics keyboards I've owned (I forget which one it was) I bought one from BCK which looked similar to the Technics SZ-E2 but because the polarity was different it worked the opposite way round. e.g: To increase the volume using the SZ-E2 the pedal is pushed forward/down and to quieten the volume it is brought back/up slightly, whereas the BCK Expression Pedal worked in reverse. (Up for volume, down for quietness)
I don't Know whether this would apply to the Yamaha accessories, but if I were you, I would make some enquiries before making a purchase. You could save yourself a lot of time and trouble.
Hope this helps - Audrey
[This message has been edited by Audrey Turner (edited 03-02-2008).]