Yamaha CS80

> > No, the reason was because the chip was designed from organ 
> tech. The 8th channel was assigned to the pedal board.
> 
> I've heard that explanation before but I don't understand how 
> that would work given the KAS logic.

Indeed.
The information I have is that Yamaha designed the GX key assigner
independently but at the same time as E-Mu, who got a patent on theirs in
1974.
It is clear the intended purpose of the GX KAS chipset was purely to drive a
fixed number of linear VCOs.
You can see the annotated service manual page here:
http://www.colinfraser.com/GX1-KAS.jpg

Cheers,
Colin