I have the DefTech SuperCube 6000. To be honest, I find the sub to be an underperformer. I thought with three "drivers", the sub would be pretty good as it should be able to displace a lot of air for the bass. What I did not take into account is the fact is that smaller drivers means less excursion as compared to a larger driver. The SC6000 performs admirably down to about 30-35Hz, but it is sorely limited below that. Using the EQ in the amp, you can boost the lower bass levels but the manual specifically states that the output will be limited. I find that to be true. Extremely low bass is compressed and output sounds soft.
I opted for two DIY subs, one a 12" Dayton Audio and the other a 15" Dayton Audio. I built the 12" sub first and I can tell you that right off the bat, the 12" sub performed as well if not better than the SC6000 at 1/3 the cost of the SC6000. The bass was lower and the output was higher. With the addition of the 15" driver, the bass in the room is now beyond what I need. The room is rather large (18x28x9') and is too big for a single sub to really "load". I used to have a Sunfire True Subwoofer, then upgraded to triple Polk PSW650s. The Polks performed well in the room, but the bass was non-existent below 35Hz.
Right now, I have the SC6000 back in its original box in the corner of the room.
If it's not a BIG screen, it's not a theater...