Adapters are a good idea. You wire them to your speakers, and plug them into the factory harness. You can purchase them at crutchfield.com. I also use ebay and amazon.
2006 GT, Strut Tower Brace, Gas Hood Struts, FR Intake Plenum cover, Metal Fuse Box cover, Moroso brake reservoir cover, Rear shock tower brace, Front Bumper Lip Spoiler, JVC DVD Head unit w/ back-up camera, satellite Radio and USB input, 2 - 12" sub-woofers, 4 - 6"x8" speakers, 2 - 6.5" speakers to replace the door subs, 3 amplifiers, LED lights under the hood and in the trunk, chrome e-handle on parking brake handle, chrome cup holder trim, and trunk lid cover with running pony emblem.