No signal from PC audio

[Caterpillar Trap]

Hi folks, I'm having an issue where channels 1/2 and 9/10 aren't receiving any signal from my PC audio. It only works when sent through main L/R. I've set up everything on the Model 12 and Windows correctly according to the manual, videos and other forum posts but still can't figure this out.

 

[mrshowboat]

on the M12 with latest firmware:
Menu, System, USB Audio, PC CH1/2->, select where you want it to go