normaly adding something like a stereo system will not **** with ur warranty I have an aftermarket amp and sub in my car and I dont expect the dealer to give me ****.

 

i bought the sub amp upgrade, and boy was it a waste of money. you can barely hear the difference. and all it does is add a little bit of bass, nothing you can really feel or anything. i say just buy an aftermarket sub and amp.

 

There is no OEM amp. The sub bridges off the rear speaker connections and has an internal amp for itself, but there isn't any external amp for the main HU. The only way to add one is by using a line-output converter because there are no preamp outputs on the stock unit.
If you add an amp this way the power output may be increased, but the poor response and dynamic range of the stock HU will remain. The best improvement in sound will be had by replacing the HU with a higher-quality aftermarket one, and adding amps to that. In either case if you are increasing power new speakers are a must.
Warranty should not be a problem with aftermarket audio equipment as long as you install it properly yourself or have it done by a professional. Use an adapter harness for the HU so nothing in the factory harness is cut or disturbed, and run independent power and ground connections for the amp(s).