Recently bought an 09 Corolla and regrettably didn't get the upgraded JBL system. I currently have a 4 speaker system with 6.5" in the front doors and 6x9's in the back. I am having trouble finding any head unit I like (nothing really matches the interior of the car). I'd like to upgrade the speakers and get an amp. Will this work okay even if I am using the factory head unit? Any suggestions for speakers and/or amp? I would like to spend no more than like 250-300$ for everything. Does this sound reasonable?