The overall speaker volume is controlled by a knob that is located between the B and R monitors. It looks like this:

The only note, in order to listen to the audio "off the heads" of the Sony BVW75 you have to patch the output of the BVW75 into the speaker in. The reason for this is that in order for the suite to be fully configureable the output of the mixer and not the recorder should be the default to the speakers.