I started by replacing my fronts with the C2's ...... they sound much better than the stock speakers, but will not solve the shaker 500's inadequacies to an audiophile. At a minimum, I would also suggest adding a subwoofer and amp in the trunck. This will create the greatest increase in depth to the audio experience. If this does not cure your itch, then you can put the C2's in the rear, put a better set of separates up front and add a second amp to run them.
Most people will tell you the JL's are over priced, this may be true, but my car sure sounds good to me. If you need any specific pointers on how to wire in the LOC's or anything else, feel free to PM me. I have all the wire color codes for what is what at the two factory amps.
2012 GT CS Ingot Silver Vert, Edelbrock E-force supercharger with CAI and 3.5 Pulley, Tremec T-56 Mag, Accufab 84.5, Centerforce DF, Billet Yoke aluminum driveshaft, FRPP 3.73 Rear, MRT Performance H-pipe, Bassani axle backs, JL Audio sound, Edelbrock strut tower brace, JPC adjustable UCA, UMI adjustable panhard bar, KW V3 coilovers, Steeda heavy duty front mounts, Steeda rear LCA's, 20" Steeda Spyders with Michelin Pilot Super Sports, Steeda Big Brake Kit ....... it just keeps going.