Thanks for the prompt reply.
The MCU is actually a hardware MIDI device "mixer" (8 switchable fader banks (channels) with motorized faders). It also has all the transport contols and various navigation and editing controls on it, that are also onscreen.
http://www.mackie.com/products/mackiecontrol/index.html
Moving the faders onscreen with mouse moves the physical motorized faders on the "control surface" (mixer) and moving any or all of the faders on the "mixer" moves the same faders onscreen. It also does a whole lot more. but that's the basic notion.