O.K I think I have your answer. This is what I would do if I were you (so it probably isnt anywhere near what you will do)
Get the HSU ULS-15 for $1099. You will get a great sub that is small yet very mighty. This will be just to get you by for a little while. Though you wont regret the buy, you may crave a little more punch after a bit. In the mean time you will have saved another $499 & you can go back to HSU & grab one of their MBM-12 subs. Now you may be thinking, "why would I mix a 15" & a 12"?"
With HSU their subs can be tuned to produce only certain frequencies. So you put the ULS-15 up front by your mains & you place the MBM-12 near your listening position. The MBM-12 is a Mid-Bass-Module tuned to pick up where your mains leave off (say 80hz) & only goes down to 50Hz. However, what it does in that range is UNREALl!! You will get slapped silly... At the same time you have the ULS-15 pick up right where the MBM-12 leaves off (50hz) & since you just free'd up quite a bit of power on the ULS-15, by releaving it of mid-bass duties, it's sound will improve even more giving you the low end you want.
Another advantage is that mid-bass is best near you & low bass needs room to breath. So having the ULS up front (or somewhere a little farther than the MBM) the sound wave has space to "stretch out" & sound very nice!
Well I hope this little tid-bit at least helps you somewhat in making a decision whatever it may be. I know you are looking to do this with 1 sub but honestly you should consider it, because you have a lot of space & to fill it properly is gonna be very hard to do with one driver. The MBM is even smaller then the ULS & can easily fit behind a couch or hidden somewhere.
Thats all Ive got for now buddy!!
