Aux channel strips can be used to create subgroups, to submix, to route a signal to multiple destinations, and as additional destination channels for multi-output instruments. Typically, you create aux channel strips as you need them. There are three ways to do this:
An aux channel strip is created automatically when a send assignment is made from a channel strip, except when the chosen bus is already in use as an input source on another channel strip.
When a multi-output instrument such as the EXS24 mkII is inserted into an instrument channel strip, several aux channel strip assignments are made “behind the scenes.” You then must create the required number of aux channel strips by clicking the Add button (+) at the bottom of the instrument channel strip. Each time you click it, a new aux channel strip is created (and automatically assigned to particular instrument outputs).
You can also create aux channel strips by choosing Options > Create New Auxiliary Channel Strip from the Mixer menu bar.