(general Firefly beginner question)

Friends,

I'm building a room-sized MIDI control surface with piezo sensors and an Arduino Mega.  This is my first entry into prototyping/Arduino and I feel like I have bitten off a lot.

I am trying to manipulate the device via Firefly, and I don't quite understand the workflow.  If I want to control variables in the arduino sketch through the grasshopper interface, what is a method for doing this?   i.e.  I have an 16-item array of integers which determines the different MIDI notes of my sensors.   They are now static, but if I wanted to put them all on grasshopper sliders, how would I write this data back to the arduino in a form it would understand?  

If this is too beginner a question, I'm happy to take pointers toward tutorials.  I believe that if I get a grip on a few basic things like this, I can fill the rest in...

Josh