Hiya Jim
Technics used to call it 'backwards compatibility' - meaning everything made in the way of a keyboard before the KN2400 is compatible with it. It doesn't quite work like that in total covering all historic models but pretty much the theory works - so if you obtain rhythm and sound registrations for the following, they should work in your model:
KN7000; KN6000/6500; KN5000; KN3000.
I guess your next question might be - where do I get those from....well it depends what sort of music you like/want to play because there is a wealth of 'style files' on various web sites, if you know where to look...
Roger M