The Mixer integrated into Usine is, of course, totally modular.
By a simple Drag & drop, you decide which Rack you want to display, its order, color, etc.
Apply a MIDI assignation with your favorite controller in a single click.
Drag a Rack over the Mixer panel to create a new mixer :
Result in the Mixer
This knob set the Audio input level.
This vertical fader set the Audio output level (-inf to 12 Decibels).
Play ON/OFF switch