I love my system to death, but it needs a sub. My speakers only extend to 45hz and are a little bass shy. In the near future, Im willing to spend ~$100 for a sub, possibly used if its not blown. Im not looking for something super bass heavy like you hear in alot of car stereos. The most important thing to me is being able to hear the bass guitar clearly and warm, yet not over-emphasized. And the sub must extend down to 20hz and up through the top of the bass range equally (flatest response possible). Thump and slam isnt too much of an issue to me, as long as I can hear it. I just want to hear the bass notes as best as possible, yet not having intrude on the rest of my systems sound signature. Also, would you suggest a built in amplifier or hooking it up to my yamaha?