Issues with USB input - Mics but no Mix*

Running Windows, ZEDi10FX

I’m running 1/8" analog out from computer to 2 1/4" ST1 stereo inputs on the ZEDi. Running a single Mic input on M1 to board.

When recording on Cubase I only get the MIC channel, when testing through Audacity I only get the stereo channel (backing tracks from comp 1/4")

I cannot figure out how to get the main mix and M1 to simultaneously send the combined mix signal into a single channel. I’m simply trying to lay quick MP3s for others to review prior to full and individual track recording.

Any and all help is greatly appreciated.