Hey, I read earlier that the factory sub sounds much better if you adjust it. Well, I did and is is a big difference. I can't tell you exactly what I did, but I monkeyed with the adjustments (gain and high cut?) as I listened to some tunes until I liked it.
It is less boomy with good response to music with electric bass lines, etc. It still has a hard time with low low bass on hip hop but there is less distortion now. Not bad for a tiny sub under the seat.
Getting after market is better, but for a stock system, it is good and meets my needs.
Plus it was fun "modding" something else on the car.