Something else to consider on that budget is getting two subs. Two
A7s-450s shipped comes to $1600, and might give you the best performance in terms of sound quality and output for your money. There are a lot of advantages to having two subs over one. It goes a lot further in killing bass nulls for starters, which is great especially if you have a large room. It also helps to smooth out the frequency response overall. You can also get two
A5-350s for $1400 shipped. That would be a massive sub setup, and I think it would have more output than the single sub solutions you mentioned. On either sub you get a nice discount if you buy two or more. You could also get two
Epik Sentinels for $1200 while it is on sale right now, when ordinarily it would cost $1600! 25% off, not bad! Personally I think you will get a lot more for your money if you go with two subs rather than one.