Strange, last week I did a live recording, used Cue Mix to send a stereo mix to a camera, no problem. Today, I could not get Cue Mix to send out to any selected out. I double checked the setting in audio set up, CueMix box checked, "Z" blue, definitely getting signal in to Studio One, but nothing going to the main outs.
I first thought it might have been an issue with how the song in question was set up, so I started a blank song, with one input, cue mix enabled for the main, out. Nothing. Checked the input level, good signal. Record enabled and source monitor enabled was fine, but with latency of course. So there's something not letting me use Cue Mix from within Studio One... But it worked a week ago...
My work around was to launch universal control first, and use that to send a signal out, and disable Cue Mix in Studio One.
Setup: MacBook Pro (mid-2012, OSX Sierra (10.12.3); FireStudio Project (up-to-date firmware and Universal Control; Studio One 3 (126.96.36.199198)