I own an XS30 (original version) and I can tell you it does a great job. The "se" versions are even better and more musical. I have my XS30 in a 3,400 cu. ft. room that is fairly open and have had no issues with its performance for room size. All that being said, you have a much larger volume to fill, and that is asking a lot for any single subwoofer, especially a sealed design. I think I'd talk to Tom about dual XS15se's for your room volume and see what he says. I don't know what the cost would be for the finish you like, so talk to Tom.
One of the problems you may have is that you are hoping for the best (as far as subwoofer location is concerned), but not preparing for the worst. The sub itself will tell you where it belongs. Many times that is not the best location aesthetically. Two subs will allow you to help get rid of room modes at the listening position, while one sub is pretty much in the hands of the subwoofer gods (a great sonic location that is also aesthetically pleasing … or right where you envisioned it).
As far as the Rythmik FV15HP is concerned. I know of no one that doesn't think it's a superb option. It's simply a terrific sub. I also understand that Brian is great in the customer service department, but sometimes short on time. Tom is simply amazing to deal with, but I swear that man is going to burn himself out! He's always available, and won't hesitate to fix any problem (even one I caused) at the drop of a hat. He's the best I've interfaced with, and that says a lot because I'm also extremely happy with SVS's customer service (I also own an Ultra) and Ed Mullen in particular.