RME Audio ADI-2 Pro User Manual page 35

Class Compliant Multi-channel mode
With USB connected all digital and analog inputs (6 channels) are routed to USB recording. In
the same way USB playback will feed all outputs separately (8 channels).
In 6/8 channel mode all I/Os can be used separately. Phones output 3/4 provides USB playback
of channels 1/2 when its Source is set to Auto (default).
User's Guide ADI-2 Pro © RME
35