Other than the Shelby/Kicker set up, I am not aware of any other plug and play solutions. Maybe Metra or Crutchfield have some adapters??
The S/K amp goes up under the right hand dash behind the glove box. There are two harnesses that come with it, one to connect to the factory amp and the other for power. For the first one you unplug the factory connectors coming from the HU at the factor amp, plug them into the S/K harness and then plug the S/K harness back into the factory amp. The other end is routed under the dash to the new S/K amp. The second harness is routed to the fuse box under the hood for power, and you're done. The S/K amp for my premium provides a low frequency non-amped signal for connecting to an amplified subwoofer. I think the S/K amp for the base stereo also has this.
When I'm done with the upgrades my car will have three audio amplifiers in it! The factory one will be left powering the 8" S/K door subs, the new S/K amp powering the four 6x8 speakers and finally the amp in the trunk sub.
2013 GT Premium Brembo
MGW, Blow Fish, AM Hood Struts
Tinted, Borla Touring AB, ProCal Tune
Full Shelby/Kicker Audio Upgrade