Hello, I've just finished a standard WSG, but now I need more sounds ! I want to modify it but need a little more exlanations about these points about your circuit :

"-4 Tone generators. Two can be pitch modulated, two volume modulated.
-4 Tone activation switches. 2 are 3 setting switches, up=on/center=off/down=volume modulation."

I don't understand where on your schematics are the two ways / center off switches. 
I found 3 spst on the electronic half schematics and in the block diagram where I suppose two of them are linked together.

Are they 2p2t or sp2t ?