I'm looking to spend in the $500-$700 range for a down-firing box sub. I'm interested in the HSU VFT-3 MK 2, the STF-3, or the Outlaw LFM-1 to go along w/ axioms speakers. It looks like the main difference is an extra $100.00 for frequencies between 20 and 25 Hz (if I'm overgeneralizing, please let me know, I'm still a newbie). Is that the only difference? How important is it for a sub to go down to the low 20's? Does it make a huge difference when watching depth charges, pod-races, and Lord of the Rings battles? Does it make Jazz, symphonies, or heavy metal music better? I don't know a lot about this, so any advice would be greatly appreciated.