Didn't put this in my first post so I want to add... after dealing with the audio upgrade in my ST3, I wish I would have bought and ST1 and done a seat swap. Other than losing the HIDs and the center console layout that I prefer (not an issue after 2014), I would have been happier with the result and saved some cash.
For reference, my brother installed a head unit, component speakers, amplifier, and a powered subwoofer in his Focus sedan. We finished the job in an afternoon. In my ST3, I upgraded component speakers, sub, power amplifier, and audio control LCQ1 (EQ and Line Level Convertor). Took me a few afternoons/evenings to finish install, cost more money, and doesn't sound as good (though it does sound pretty good). His setup sounds better primarily because I am stuck with MFT/Sync factory system as my source. He has more control at his source and his head unit has bluetooth, backup camera, and gps. He installed a quality head unit which I suspect gives his system the sonic advantage.