The trade-offs for subs; if we hold driver size constant at, say 10", are enclosure size; enclosure type, ported or unported; amplifier dynamic power and how much if any equalization (boost) will be applied (internally by design); and frequency bandwidth required.
As an example. An 10" inexpensive home theater in a box sub> 2 cubic foot ported enclosure, 150 watt amp and no boost applied. The speaker will play at about 102dB max and might have a frequency response of ~45Hz -6dB to 100Hz. There will be no user adjustable single band parametric equalizer available and the system, not having good low end extention might need to be moved around so as not to excite the very common single room mode frequency.
Make the box really small, like 0.6 cubic feet internally, and use a very expensive 10" driver with a long linear throw and you need lots more power and a low frequency boost circuit within the amplifier. And, you need a LOT more power. But you can get a spec like the CSW-10 has of 27Hz -6dB at 105dB along with the luxury of putting the system into a corner if you want to take advantage of the extra 6dB of gain you'll get from corner placement. Note that the only reason you can do this is because you've got that built-in RABOS single-band parametric which should be able to easily dial out that single peak you'll almost assuredly get since you've now excited your room in a most efficient way.
All system parameters can be input into a design program like LEAP so the design engineer will know what to expect before the model shop even builds up the first box. That's how it's done.
Having said all of that, your room is quite large and I'm a big fan of multiple subs. So if you do have the luxury of moving your subs around to their areas of least room mode excitement (and you're willing to put the time and effort into this proper placement) I would certainly recommend two less expensive subs which might have larger enclosures and correspondingly less (required) amplifier power to achieve the same relative low frequency extention and SPL. From the test reports I've seen on at least one of the SVS subs I'd say mtrycrafts' recommendation might be a very good place to start.
