Surround master channel strip
When you set the output of a channel strip to surround, a surround master channel strip is automatically created in the Mixer. The surround master channel strip processes signals routed to the outputs configured in the Surround preferences. For more information, see Set surround preferences.
You can insert surround effect plug-ins into the master channel strip. You can also use the Down Mixer plug-in to quickly switch between input formats.
Important: As soon as the surround master channel strip appears, the Insert slots of the individual output channels are hidden, and any existing effects in the Insert slots (of output channel strips) are no longer processed. Logic Pro X remembers the insert configuration, so when you remove all surround outputs, the original output channel configuration is restored.