I have nothing but positive things to say about either the Seaton Submersive or JTR Captivator S2, but a S2 is obviously going to have more output than a single Submersive HP unless you do the slave option and run two of them. Having heard both on many occassions.
Both are excellent subs, and most would be happy with either option. I do think either would be better than what you have.
However. Lets take what you have said you are unhappy with and discuss further. The JL Fathom 113 is not a slouch. It is about the equivalent of a SVS SB13 Ultra which is also not a slouch. The amount of 'headroom' you gain by going to something like a single Seaton Submersive HP may not make you satisified. Perhaps, even a single S2 may not suit you for home theater use. You find many guys around here going with four or eight 18" sealed subwoofers for movie use. I've found that even four SI 18" sealed subwoofers don't have the real world output of my two JTR ported captivators when I tried carp's in my room. In the ULF thread it says I'd need six 18" budget oriented subwoofers to have the same output....that's been pretty accurate according to my experience.
If you are 90% home theater - perhaps a pair of ported or horn subs are more up your alley. They have nearly double the output around 15-20hz tune as a single sealed counterpart. In movie use unless you do several sealed subs --- your experience is probably typical - in that you might desire more output. I have a couple ported JTR Captivators that I am very pleased with - even after 2.5 years of ownership.They would have SIGNIFICANTLY more output than a single Seaton Submersive, or a single S2 at about 17-25hz which is where your single sealed Fathom 113 is probably failing to meet your expectations. Just food for thought.
I'm a big fan of at least two subs for room frequency response smoothing, and I'm a big fan of ported or horn for movie use. If you are going to go big sealed - you'll want multiples - two F113's might not be enough. If you are going to go big 18" ported (with a quality sub) - two will likely do quite well in that size room. My room is about 3500 cubic foot for reference.
http://jtrspeakers.com/home-audio/captivator/
Both are excellent subs, and most would be happy with either option. I do think either would be better than what you have.
However. Lets take what you have said you are unhappy with and discuss further. The JL Fathom 113 is not a slouch. It is about the equivalent of a SVS SB13 Ultra which is also not a slouch. The amount of 'headroom' you gain by going to something like a single Seaton Submersive HP may not make you satisified. Perhaps, even a single S2 may not suit you for home theater use. You find many guys around here going with four or eight 18" sealed subwoofers for movie use. I've found that even four SI 18" sealed subwoofers don't have the real world output of my two JTR ported captivators when I tried carp's in my room. In the ULF thread it says I'd need six 18" budget oriented subwoofers to have the same output....that's been pretty accurate according to my experience.
If you are 90% home theater - perhaps a pair of ported or horn subs are more up your alley. They have nearly double the output around 15-20hz tune as a single sealed counterpart. In movie use unless you do several sealed subs --- your experience is probably typical - in that you might desire more output. I have a couple ported JTR Captivators that I am very pleased with - even after 2.5 years of ownership.They would have SIGNIFICANTLY more output than a single Seaton Submersive, or a single S2 at about 17-25hz which is where your single sealed Fathom 113 is probably failing to meet your expectations. Just food for thought.
I'm a big fan of at least two subs for room frequency response smoothing, and I'm a big fan of ported or horn for movie use. If you are going to go big sealed - you'll want multiples - two F113's might not be enough. If you are going to go big 18" ported (with a quality sub) - two will likely do quite well in that size room. My room is about 3500 cubic foot for reference.
http://jtrspeakers.com/home-audio/captivator/