Presonus Quantum - Second pair of monitors main volume knob

I am willing to buy a Quantum, but have a question about dealing with a second pair of monitors.

Is this possible anywhere on the front panel to choose which output should be used and controlled with the main volume knob ?
Or is the main volume knob exclusively used for the mains ?
If yes, then how could it be possible to control (sound output + volume) a 2nd pair of monitors ?

Thanks for the feedback.

Regards,

S.