Hi, I am thinking about getting Hsu STF-2 sub from CompUSA. It obviously has rave reviews and excellent price (350-). However, I was curious what is the difference between this sub and VTF-2? The latter would be 150$ more and has something called "Line level low pass for 2 channel systems". Can somebody tell me whether VTF-2 is much better than STF-2 to justify spending extra 150$ and what does this line level low pass actually do?