The above poster is correct that if you don't have bass traps or some other way to minimize the bass response in your room then you should do that first. All rooms have large peaks and dips in the bass region depending on the dimensions of the room. I use a Behringer DEQ 2496 to tame all my room modes from the bass on up. This is in my dedicated and fully acoustically treated room. Room acoustics play a huge role in the sound, especially in the bass.
If you decide to upgrade your sub after this be sure to look at Vmps subs. They're extremely musical and powerful. More importantly to some is that the prices are excellent. Please be aware I became a part time dealer for Vmps earlier this year but that is what I'd owned for many years. Do some research on subs as you'll find there's alot more good subs out there than the two you listed. Another favorite of mine for the money are the used M&K subs. For 5 or 600 bucks you can get a good sub. Be sure to learn about those room acoustics, most people consider acoustics last when in reality it should be first. Good Luck
