I wish I had a QU32 wayyyyyyy back when I was in high school.
I just used my QU32 for two school plays I do sound for.
The AMM works great but is only available on the first 16 channels. Short of going into the settings there is no way to just toggle it on and off unless you make up two scenes and do a block on most other parameters. A scene recall will produce a very brief muted audio output.
How many people are singing at one time?
Are you riding the main faders per the lines spoken during the play?
In the AMM menu go to the setting tab and turn on the follow fader function.