I am not sure if the Shaker system works like the Bose system in other cars does, but if it does, it will take some extra work to get a new amps to work with the entire system. If you are planning on ripping out the Shaker system and even considering installing a new head unit, the process is pretty basic. It really depends how crazy you want to go with everything. For example: I bought my 2014 with the basic sound package because I knew that I wanted to build my system from the ground up. I went with Alpine Type R door speakers up front, custom-fitted Kenwood 3way 6.5s in the rear deck lid, an Alpine 4 channel amp for the speakers, two 12 inch Kicker CVR12s in the trunk, two 1.5 farad Rockford Fosgate Capacitors for the subs, and an old Performance Teknique 2 channel amp that I had laying around for the subs. I also installed a Pioneer double din touchscreen head unit and got rid of the Sync feature that I found annoying when trying to stream Pandora from my phone.
Everyone compliments how clean and well-rounded my system sounds when they ride in my car and I am extremely satisfied with the sound quality. Any higher name brand speakers should work well for you, but I'm sure some members on here can get even more technical about which speakers work better for crisp or melded sounds. I have personally had great luck with Alpine, Kenwood, Rockford Fosgate, and Infinity door speakers. As for subs, it depends what kind of music you listen to. I listen to everything from Country and Rock, to EDM and Dubstep, so 12 inch subs are great to handle that kind of range. If you listen to mostly Rock, Country, Jazz, or Indie two 10 inch subs would work great. If you listen primarily to Hip Hop, EDM, Dubstep, and other genres that involve heavy bass, you can go with 12 inch subs (my recommendation) or even 15 inch subs for an extreme amount of bass when coupled with the right components. Kicker CVRs are great subs. I have also had good luck with JL Audio, Kenwood, Infinity, and Alpine subs, but I seem to like my Kickers the best. I installed two capacitors with my amps that act like batteries that store and help evenly feed electricity to my amp because I am running a large amount of wattage through my amps and it prevents my headlights from dimming every time I play a song with a lot of bass loudly. I hope my info helped a bit and feel free to ask away if you have any more questions. I once knew nothing about stereos myself.
Eibach Pro Kit, Dual Flowmaster 40 Series Axle Backs, 18" Milanni ZS-1s, 245/45R18 Falken ZE-950 Tires, Smoked Front Marker Lenses, Limo Tint, Pioneer Double Din, Alpine & Kenwood Speakers, 12" Kicker CVRs, Alpine Amps, AM Paint Matched Side View Mirror Caps, LED bulb conversions everywhere
, more to come... need to sell OE wheels/tires and suspension first.