I know I don't want to change from my stock head unit. So I was wondering, what do you guys think is the best combination woofer / amp for the price. Also what size do you guys think is best for a coupe? My friend said get one 15", but maybe I want two 12". And comments? Not looking to spend a fortune. Also, will I be able to hook up an amp and more woofer into my existing head unit?