USB Audio Input Issues

Hello folks. I am trying to sample audio from USB (my DAW) to the S2400 and I am not getting a signal. Currently I am doing some live looping and have selected USB as the source. When I hit the pad and attempt to play something I don’t get any signal whatsoever. I’ve tested the same method from the analog inputs and I get a signal from other instruments. This is made even stranger by the fact that the S2400 is slaved to the computer - all transport comes from the DAW. That means that the two are clearly connected via USB, but just no audio. I have tried via the sampling function as well, but get no sound.

Has anyone encountered anything like this? Can you help me get audio from my daw to the S2400?