Ian, I can remember experimenting with this sound design around the early 90's..
We use to velocity switch the 4 partials of a tone[on a Roland D-70],..giving us 4 elements of a sound..and the D70 would go one step further..allowing, 5 of these 4 partial tones within a performance..all velocity switched..again...at 31 polyphony it could be tricky...