Hi Anthony, I think you are right about the lack of any mention of the Expansion boards in the KN7000 Manual. The only reference I can see, is the Selection button in the pictures of the front panel.
The sounds in the Expansion boards are in Wave Memory chips and are not transferrable. When the boards are installed in a KN7000 and an expansion sound selected, the operating system just 'Points' to the sounds stored in the wave ROM, on the boards, rather than the normal internal wave samples.
After silence, that which comes nearest to expressing the inexpressible is Music.
( especially when the music is played on a KN7000....)