Hi the expansion boards are more voices/sounds to play with,on the KN7 there is a panel you can remove on the underside of the keyboard and it has 4 slots into which the boards fit.On the main control panel you will find a button marked"EW Expansion" when the boards are fitted this opens up a new page with a list of sounds which can be used anywhere on the keyboard ie:- Right 1/2,Left, any part in composer or sequencer thus adding to the 1187+ sounds you already have. By fitting all 4 boards it takes the on board sounds to well over 2000 and that's without using voice edit!!!
Best regards John.