Hi, Welcome to JustAnswer.com, I am glad you are here! My name is Eric & I will endeavor to answer your question.
Though you have asked this in the Home Improvement Category, It should probably be asked in a category named "Professional Sound Reinforcement". JustAnswer however, has no such category. That said, I have been working with bands and doing live sound for 36 years and personally currently own one 12 channel Mackie, two 16 channel Mackies and a 32 X 8 channel Allen & Heath mixer.
In order to accomplish what you need to do, you would take the main outputs from the slave or sub mixer, and input them into two channels for example 11 & 12 or 1 & 2 of the main mixer. The main mixer would be able to control the overall volume (in the house mains) of what the sub mixer sends, but the person controlling the sub mixer would be able to control the overall mix of whatever was input into the sub mixer.
The technician on the main board would not however, have any control over independent monitor mixes for sends through the sub mixer. The monitor feeds for whatever is sent into the sub mixer would have to be individually controlled from the sub mixer.
This is great thanks I have a 12 Mackie as I said before and a 16 channel Allen & Heath
So to get my head around it all The feed into the main mixer would be panned left and right Like the feed into channel 1 to the right and in channel 2 to the left
Exactly! You understand the principals of this pretty well as it is. I am glad to help you confirm what you already suspect.
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