Input preferences are only available when Additional Surround Options is selected in Advanced preferences.
These preferences let you set the surround format.
Surround Show As pop-up menu: Sets the surround format. The choice you make automatically updates the remaining pop-up menus in the Input pane.
Surround Initialize buttons: Choose between the default setup of Logic Pro, the ITU (International Telecommunications Union) standard, and the WG-4 standard.