It's not JUST about amp power, it's also about driver excursion. You need to move air to make bass, and more air for lower bass. A big box gives you a lot of air to move. A driver that throws 3inches linearly, will move air too. The big ported boxes are more efficient, not to mention the vents will help keep the driver cool. A sealed high output sub that plays low needs a well engineered driver to work in that environment and that cost's money.
You want bass without the space, get a proven sealed sub (Digital drive series is all that comes to mind with low bass, but you'll need the DD15 at the least.) or convince the better half to increase the size. Every ported sub in SVS's line up should hit 16Hz.. some a little louder then others, you don't need a /2.
SheepStar