Essentially, in one instance of MUX, you create a 'send' module and assign it a 'channel' value. Then in another instance of MUX, you create a 'recieve' module. By assigning the 'recieve' module the same 'channel' value as the 'send' module, any audio data plugged into the 'send' module is sent through a virtual wormhole to the 'receive' module.
Its actually not a new idea, and I have actually requested it in a few other software packages over the years, but nobody has ever implemented it AFAIK. I know it is technically possible though as there are some plugins that do this sort of thing already (SKNote has one I think).
The obvious use is sidechaining, but I can think of a whole load of others
