This is an expander for Bartender and Barback, enabling CV control of the level of the send bus of up to 8 channels.

Each section of four jacks has a cable to connect to the mixer modules.  To get 4 channels to work with Barback you want to connect it to the last Barback in the chain of two.  It will then pass along channels 3 & 4 to the next Barback.