Do you want a button on the MFC, or an expression PEDAL?
Keep in mind that each X/Y will be independent. Meaning, Amp X/Y will be different than Cab X/Y etc. You will need a separate controller button (CC command) for each one.
I suppose you COULD go in and change the cc value for all of the X/Y's (or a selection of them) to the same number, and have them all change on the same signal... that might work (don't know, never tried it... but can't think of why it wouldn't work).
For an expression pedal, you would set it up so that values above a certain number (like 60 ) would be X, (or "on" )and values below that number would be Y (or "off") Assign that pedal to the CC number of the X/Y state you want to affect, and that would work.
BUT... By FAR the easiest way to do this is with SCENES. Read the manual or Wiki about how to use scenes if you haven't already. Then you can change X/Y states in any order you like for as many blocks as you like, each with it's own setting (X or Y) independent of each other but changing all at the same time. A much better way to go IMO.
Also, by adding use of scene controllers, you can really open up the horsepower of changing an amp or effects settings, and that way you can get much more than the 2 available X/Y settings. (example: Scene 1 drive = 1.5, Scene 2 drive = 4, Scene 3 drive = 7.) That's like 3 amps right there, all done with scene controllers.
