Sounds easy don't it....chuckle....
and you are thinking of buying a second hand KN2400 or KN2600 which may or may not have the original software with it to enable these files to be transferred either by floppy disks or USB connection to whichever of these two keyboards you buy.
Straight out of the box straight into cubase I think you said - with either the KN2400 or KN2600 secondhand you may find that you experience a significant gap between opening the box and commencing to use cubase...
Rog