You select the control bank to select which group of 8 (or whatever) tracks the controlls actually control. You should read the user documentation for some products like a Mackie MCU Pro and Avid Artist Mix, I would be very hesitant about problems and poor support from Avid with any Artist series product.
You are already working with Pro Tools in the box (just using a mouse to control things) right? Able to record and mix stuff, and are sure you need a control surface at all?
Here are some control surfaces. If I had to get one in this price range it would probably be the Mackie
http://www.sweetwater.com/c808--Mixing_Control_Surfaces