I was very unimpressed with the Shaker 500 system in my 2011 GT, but wanted to keep the head unit for a few reasons (sync, a/c controls, stealth look, cost, etc).
I ordered a 4 ga wiring kit and a Scosche line output converter from Crutchfield and installed everything, tapping the LOC into the rear speaker wires. I ran the power wire through the fender well on the passenger side as has been posted before.
Some more research led me to the MTX reQ. This device works as a line output converter, but also adds bass as the volume increases, overriding the factory EQ settings.
So, if you had just bought the reQ first, you wouldn't have needed the Scosche LOC?? Sorry if that's a "no-brainer" question, but I know almost NOTHING about car audio.
Delivered 5/4: 2012 Mustang GT Premium Grabber Blue 401a w/ Grabber Blue stripe - Brembo, 3.73, Comfort, HID, Security w/ reverse sensing, backup cam
Mods: H&R coilovers, BMR adjustable panhard bar