iConnectivity AUDIO4c Desktop 4x6 USB Type-C Audio/MIDI Interface - Manual (Page 24)

Stream mode output with USB1 mix visible with [Stereo] selected. USB2 mix options are identical to
USB1 mix options in Stream mode. A computer is plugged into USB2. USB2 channels 1 & 2 are seen
metering in the bottom row.
AUDIO4c User Guide v2021-0002 Page 17