I'm all new to this car audio stuff so I'm a little lost. I have a 2002 Jeep Grand Cherokee and i bought new speakers for my front and rear doors. my fronts are 6x9 Boss speakers and my rears are 6.5 Boss speakers. I wanted it to be louder and not to sound like crap when i turn up the bass and treble. It now sounds good except it's the same volume limit as the stock speakers. The rear ones are 400w a piece and the fronts are 350w a piece. Shouldn't the volume be able to go a lot louder than my stock ones? is this because I have a stock head unit? Should i get an amp?