From this page of MENU, you can set the EXT. input source. This function use to send the LINE input selected to the STUDIO or
CONTROL ROOM loudspeakers like BY-PASS. You can select one of LINEs list (LINE-1, LINE-2, LINE-3, LINE-4, LINE-5, LINE-6 AND
LINE-7) to set it like EXT.INPUT source by following these steps MENU > AUDIO > SETTINGS.