Of course! I read to fast and didn't pay attention to the zoom part of the problem.
Sorry!
But using a tool like loopback to pass the audio from qlab to zoom should give you an extra software layer to dynamically and quickly change your audio levels during the rehearsal.
Without knowing your setup, if you don’t have an audio interface that can do this by itself then here is a quick and dirty method: Install a virtual audio driver such as Blackhole (free) or Loopback by Rogue Amoeba (paid), send QLab’s audio output through the virtual driver, and set the virtual driver as the “mic” input in Discord. (Same for Zoom, or whatever you need).
Just remember: Good, fast, cheap? Pick two.
Take a look at bitfocus Companion and an Elgato StreamDeck for controlling QLab. You can control QLab via OSC commands and it has feedback on the StreamDeck from QLab.
Companion software is free. Download it here:
https://bitfocus.io/companion/
StreamDeck at Amazon (though I am sure you can find it in plenty of places:
There is also a Companion User Group Facebook page is helpful.