Last night i used 3 sis in a patch that you could think of as a 3 band eq with adjustable resonance. 3 sis mode, span and quality settings will all have an effect on the patch output. (Of course)
Signal in to the ALL input, signal also in to a summing mixer (coldmac works)
Signal from HIGH, MID, and LOW into attenuverters.
Attenuverted signals to 3 other inputs on cold mac.
Attenuation/inversion will add or subtract the bands from the original signal.
I usually just mix the 3 channels together, so thus was an interesting change!