The Apogee Gio is a pretty neat piece of hardware, it functions as an audio interface and a midi controller. It should work fine along with MainStage and Sunday Guitar, you will just want to assign the buttons in Layout mode to control different aspects of the template. It does have an expression pedal input, so you may look into getting an expression pedal that you can use as a volume pedal, especially if you plan to do any swells or ambient guitar stuff. You'll want to make sure that your OS and version of MainStage is compatible with it.
