2002 Ford Focus factory radio remote amp turn on wire?

O.K, I know that there is not a factory amp in the car other than the one in the head unit. I am looking at putting in a "stealth" system that will utilize the factory radio/CD unit in the dash, with a large dose of signal processing from Audio Control. I already have the line level signal tapped off of the now defunct speaker wires. Q-form kick panels with Boston Acoustic separates, 12" (Boston) subs, with 2 Soundstream amps under the seats in fan cooled stainless steel boxes. Here is the the sticking point - which wire should I use as the remote turn on? There is no power antennae wire, no remote wire that I have found or seen on any diagram. I hate to have to tap into an unrelated circuit to use as a turn on switch. Any ideas? Has anyone run into this before? When I called an installation shop (higher end) they said "bring it in". No s**t, I'm sure they can do it and charge me, but this is all being done by myself (with your help) in my garage. Thanks.