This is what I usually do with my keyboards. Always playing spontaneously and live. The Vsts are controlled from the upper keyboard, while the Giga sounds from the MS's keyboard itself. All the keyboards are connected to the MS via Usb where I can link them as I wish using the Jack.
I only want to show you how I use the MS and how it can be the main controller in the studio.
http://www.youtube.com/watch?v=94ahHCszEwc