[Anthonyc77]

First of all stock speakers sound good enough, why you'd want to change them and "leave" the stock headunit is beyond me. The speakers are going to be underpowerd, which can lead to high volume distortion, etc. (not too familiar with what happens, by why have underpowerd speakers anyway? The stock ones are pretty loud.)

As for the warrenty, if you change the speakers, then no more speaker/headunit warrenty, so might as well change the stock headunit as well, fully power the aftermarket speakers, and enjoy actually upgrading your car system.