Apple Logic Pro X - Manual (Page 513)

Chapter 16 Mix a project 513
An aux channel strip is created to the right of the multi-output instrument channel strip. Use this
new channel strip to isolate and route a sound for independent mixing and processing.
4 Repeatedly click the Add button (+) to create more aux channel strips, for all stereo or mono
outputs available to the instrument plug-in.
You should create only as many aux channel strips as are required for the number of outputs
used by the multi-output instrument.
After you create the first aux channel strip for your multi-output instrument, a Delete button (–)
appears beside the Add button (+).
Click the Delete button (–) to remove aux channel strips.