Bluetooth for ALPs

[ttNB]

Ok, so I recently put an order in for the Bluetooth connection for my ALPs (from BRD) thanks. I was wondering (I don't have it yet) how does this work? What are the connections being made? From what I read they all say something different. Like the no connections needed to be made through the firewall and some say you don't need the controller. But where does the main unit go? If it has to stay in the cabin space, you still have to fish the wiring through the firewall. And you still have to keep the CPU because of updates, correct? Any info would be greatly appreciated. Thanks.

I have a dual system.