Heres the deal dude, normally you would tap into the automatic antenna, which when the radio is on gives a constant 12V to put up the antenna... since the Aero doesnt have an antenna (correct me if I'm wrong).. you cannot tap into this... the easiest way to solve this is to splice into the power cable (running to your amp) and install a toggle switch, and you'll have to turn it on and off manually... I can give you more detailed instructions if you need...
The Aerio does not have a switched power wire in the factory connector plug, the factory sub is always powered with the key on, it has a signal sensing circuit that switches it on when there is an audio signal present.
If you are brave, there is a switched 12 signal in the Ce-Net connector (the square plug you would connect a CD changer to).
There are 2 larger terminal connectors in the plug, one is ground and the other should be a switched 12volt.