I won't argue with any of the good advice already offered.
I did not know that Jason upgraded from the EP600 to EP800. I was able to hear the PB13 Ultra and the EP600 at his home one evening, and concur with the comments presented here. Both subs were fantastic, but they also sounded distinctly different. I preferred the greater perceived articulation of the Axiom sub, and expect that the EP800 would be significantly better yet.
We are a whole community of "that guy" - StPatGuy