We had the exact same issue yesterday streaming our church service. Was listening to the monitor audio and thought everything was ok. The master was muted so our viewers heard nothing and were posting like crazy that there was no audio. Was really short handed so it took a while to realize the problem and even longer to realize that the master was muted.

Would REALLY love for the monitor to be post all audio processing so we can hear what the viewers will be hearing.

I figured out a work-around to this problem. We have a pretty simple setup, so the work-around may not work if your setup is more complex.

Inputs:
PTZ Camera
Audio mixer board
Powerpoint slides
MP4 video

I ended up connecting all audio inputs to channel A as well as the Master output. I configured channel A output to a set of headphones. Enabling channel A adds its fader to the internal mixer. I configured the Master and channel A outputs identically using the Gear, and set their faders to the same levels.

Since our setup is pretty simple, we balance the individual mics attached to the sound board on the sound board. I can now adjust the sound board input slider and monitor vMix output using the channel A headphones. Same goes for the audio level from the MP4 video input.

Greg Y.