My moms got a 10in sub in her car with her stock headunit. We kept the headunit cause the car came with a 6CD changer. The only thing i dont like about her system is that with the sub the bass over powers the stock speakers in the doors. It sounds great with CD's but the radio sounds like sh!t. Shes got aftermarket tweeters also. I just think she needs a different headunit to give the stock speakers some power.

My headunit has the LOUD button but i dont use it cause it makes my speakers get distorted (aftermarket speakers too) So i just keep it off and turned my amp up. I think it sounds better and i have more mid's (voices) and also more highs

Im still thiking of getting a 4channel amp but i think it sounds great now