It would be helpful for different options for main out, all being controlled by LR out.
The options that would be nice to see would be:
LR
LRC
C
By default, C should sum LR.
It would also be nice to have a LR+M output so the mono can send to subwoofers. Even better if that output had a low pass option.
Why would you want to use a generic 12dB lowpass for your subwoofers? Don’t you have specific procesaing gear, also called a digital loudspeaker management device, for that?
Not in every situation. Many smaller theaters I have worked at feed the Center or Mono bus right into the sub’s amp.