I think that you will have a hard time getting the most out of this midi controller if you are only going to use it with Garageband.
For a program that is free with a new Apple computer, Garageband is a decent program. But it is a very basic entry level program and intentionally limited in its scope.
I don't think that you can midi map with Garageband. My midi keyboard has a pitch bender and a volume slider that work just fine, and I know they sell specific hardware with transport controls for garageband. But all those other knobs and sliders, whatever they are for, I don't think you can get them to work.....
I just did a quick search and found this on mAudio's website.