Some confusion about Control Room setup


I’m trying to setup Control Room with my UA Apollo and a DBox. Basically, I want the main mix to go through the Apollo’s MON L and MON R outputs and then have a Cue mix I can send via the Apollo’s SPDIF outputs. Then I can control which one I hear (and the vocalist hears) using the DBox controls.

In Cubase, I’ve set up 1 single Stereo output that isn’t connected to any hardware connections. In the control room set up, I have 1 monitor output that goes to Apollo MON L and MON R and 1 cue output that goes to Apollo SPDIF L and SPDIF R. When I listen to MON L/R vs. SPDIF L/R via the Dbox, I can hear the difference of the listen levels I can set in control room. However, the Cue values on the individual channels don’t seem to affect the cue mix at all. I noticed that the routing of the channels is to “Stereo Out” and if I remove that as the output for the channels, then the cue values make a difference, but when I switch back to listen to the Main Mix, I need to put the channels output back to Stereo Out. Is there a way to avoid that? What am I doing wrong?

Thanks for your help!