Try to pick up the September issue of Sound&Vision magazine. Of the 5 subs in the ~$800 price range, the XV15 was the output champ. Using CEA 2010 measurement Low Bass, the XV 15 put out 125.from 20- db (from 40-63Hz. For Ultra Low Bass, (20-31.5db, the XV15 measured 116..2 db. Unfortunately, listeners have varying priorities. Some listeners might favor the sound of a sealed sub for various reasons. That is why Power Sound Audio also sells sealed subs.
If you want the deepest, loudest bass for $799, the XV15 is hard to beat. From the article., The whole room pulsated almost as if sort of monster had plucked my house off the slab,and began shaking it like a toy.'
In the article, some of the listeners, (besides Brent Butterworth) who were part of the listening panel, had other prefereneces in the group of 5 subs. So, if you want house shaking bass, the XV15 should please you.