Hi Mario,
This is just a guess , but I would say that the files should be interchangable.
I know you can take a "clavinova" disk and it works with the Y2K . I think , where they are both "Yamaha" they should work together. As far as "regestration memory" that is a very good question. Did "Yamaha" learn from the Y2K or is it in there eyes the "perfect way to save" !!
I think we`ll have to wait and hope that "Yamaha" has seen the error of there ways
Take care, best of luck
jedi