Just for giggles, I throw my measly 1 cent's worth .... as I know the "internet" direct subs are all the rage. I'm in process of building a "media" room, but is also somewhat a dedicated theater; the room is fairly large. The two 16 inch, "internet" plate-amplified subs could not begin to charge the room. Enter a new JBL 5628 Cinema Sub (same drivers as Sub-18, but 2) and a used Crown Macro-Tech 3600Vz. Problem solved. With some experimentation, it was not as hard to balance the three subs as I feared. I will tell you this .... no active consumer sub is going to hit you in the chest, like those subs driven by some good, high clean power. After a week's use, frequency response smoothed out and sounds pretty good. Price with a used Macro-tech amp ? 1.5 times the active internet sub. I consider that a bargain, for what it delivers. The two Sub-18's would give you two cabinets obviously, and more possibilities of placement for balance; the 5628 is like a refrigerator. My humble opinion .... If you have the room, go for the 18's, and put a real amplifier behind them. You wont regret it.