I have 2012 GT base model. I have changed the front and rear speakers. Look into the AudioControl L6i, paid $113 on Amazon. It connects to the speaker output from the HU and converts to a 9.6 volts output via three sets of RCA connectors. The third set can be used for a subwoofer. A higher line output gives the amp a cleaner signal and your amp is more efficient. I have installed this unit and I can tell a big difference.