Of the three brands you have listed, I'd rank them for subs:
Epik SVS
Klipsch
However, I think you'll find the Epik and SVS are on a whole 'nother level compared the the Klipsch. Check out Elemental Designs as well, for good performing, reasonably priced, high output.
Personally, I have an Epik Conquest (their previous model series, largest). The build quality is solid, and the customer service was top notch when I dealt with them. The output on this thing is amazing, but it is tremendous. Their newer subs, like the Dynasty, are smaller. Generally positive reviews though.
Check out AVSForum. Loads of Epik owners there. They have a thread in the Subwoofers section.
Epik's owner is a Chad Kuypers who is a member here. His amps come from Indigo Technology of Canada (BASH). His drivers were designed and built by Scott Atwell of Fi Car Audio (former owner of Resonant Engineering). That's a lot of great ingredients and all Chad has to do is design implement them into a proper design which a LOT of customers think his has done.
And if you call Epik you will probably talk to Chad's father. It's a family business in the north Chicago suburbs.
I spoke to Epik a week ago and they are no longer using BASH amps in any of their subwoofers. I am a little uncomfortable that they use a 600 watt amp in all 5 of their new subs.
The Conquest will probably not come back, but they are looking to see how they could source a 1,000 (or even 1,200) watt amp, IF they decide to bring the Conquest back.