Hey, you'll not get criticism from me! I might be in the minority but I actually even like the aesthetic of the Monolith subs. That angled blockiness makes them look powerful. They're great subs and I don't think they're overpriced either.
Yes, that's in my room using REW for measuring. First I run Audyssey, measure, generate some filters with REW and upload those to a MiniDSP 2x4 HD and apply. Then remeasure and lightly manually tweak it from there.
I'm pretty flat to 15 hz and that's plenty for me. I'm sure yours is at least equally capable, possibly a bit better. When I play tones below 20 hz I can't hear them anyway. Why the need for 12.5 or 14 hz? How much material do you have in that range? A flat response that low is a pretty tall task and usually costs more than I'm willing to spend.
I'm just curious is all. Maybe you have a pipe organ music collection or something? Whale songs? Elephant calls?