Here's what I know first hand. The Kicker subs are pretty much plug and play with very little mods needed. Great quality and sound. The factory Shaker amps do not have enough to drive the kickers like they do the stock subs. The stocks have a lower ohm rating than the Kickers. Shelby/Kicker also offered a replacement amp for the door subs that gets mounted behind the glove box (Also plug and play). Its a bit pricey @ $400+. I have not been able to find one for less and for that reason I have held off on the purchase. I also know that all of the quality 8" sub replacements will require a better amp.
2007 Roush Stage 1,Roush Stage2Suspension,Bullitt Strut Brace,RoushCAI,BrenspeedTunes,RoushAxleBack Exhaust,SteedaUnderdrivePullies,SteedaSSBrakelines ,MGWshifter,PaintedRearAxle,Carbon FiberInterior,Leather, Stripes,Alpine CDA-9886 w/BostonAcousticsSpeakers/Shelby Kicker Subs,Sirius, BMR Adj Panhard Bar,CHE K-Member Brace with Torque Limiters,3D Carbon Eleanor Grille,Optima Yellow Top,RadiumEngineeringCatchCan,Shaftmasters Driveshaft,UMI Traction kit,StopTech slotted Rotors,EBC Reds.