I am a Hsu owner, never heard any svs subs. At that price there are so many great subs available. I am glad I am not in your shoes.
If you want an accurate powerful and very well designed sub, the HSU VTF3 MK2 would be my suggestion. It can go down to 16Hz, cost about $650 and the upcoming **turbo** upgrade later this summer at a small cost will take this award winning sub to new highs.
Or if you can wait a few more months, get the upcoming VTF3HO. Still well within your budget, and one of those beasts will equal or better 2! TN1220s
I hope I was helpful. Good luck and if you can,
LISTEN to as many subs as you can. They don't all sound alike.