I did similar to Kato, but added the Shelby Kicker rear speakers and the Kicker rear sub that tucks into the right corner of the trunk. I also added the Shelby-Kicker amp that fits under the glove box out of sight. It was all plug and play, super easy installation. One note, if you replace the 6x9 door speakers you will need to buy the 2012 or earlier adapter rings as the 2013+ OEM speakers have integral adapters.
2013 GT Premium Brembo
MGW, Blow Fish, AM Hood Struts
Tinted, Borla Touring AB, ProCal Tune
Full Shelby/Kicker Audio Upgrade