Sum+Inv

Two identical channels with two inputs and two outputs.  For the first output the two inputs are summed (at unity) and the second output the sum (at unity) is inverted. 

The second channel is identical to the first channel but it normals channel one summed output to the first input.  This enables a 3:1 configuration with both a summed and inverted output.

This is a great companion to the COCO system.