Subwoofer hunt

I don't think you could go very wrong with your original choice, the JL E-110's. I have the Focal Sopra No. 2's paired with dual JL F-112's, and it's a sublime combination. (My room's about 400 sq ft.) A single E-110 would probably be enough for your size room. You could always try it out, and add another if you're not totally happy with it.

My two F-112's have had no issues for the past year. The amp fuse on one did blow, because of a failure on my receiver's muting circuit. Even though it was no fault of the sub, JL covered the repair (which was really just replacing the fuse) without any complaints. I'm sure if you actually did have an amp failure, they'd take care of you. The overall quality of these subs seem great.

I don't have any experience with the SVS or HSU (I've heard the REL's, was in a totally different setup and room though). Do they sound as good as the JL's? Maybe. I think part of what you're buying with the JL is their reputation, and quality (built like a tank is the best way to describe it). The black gloss finish is good (not as nice as on my Sopra's), about the same as what you'd see on Velodyne subs.

Good luck, I'm sure you'll love the subs, no matter which brand you go with! I do strongly recommend to go with sealed, I've had bad experiences with non-sealed designs in the past (especially for music).

If you are looking for musical truth, the Vandersteen approach of connecting the subwoofer with the assistance of a high pass filter directly to your amplifier's output, is a fine way to go. By feeding the subwoofers with the amplifier's signal mates the subs. sonic character to the sound of the rest of the system  When set up properly, it should just sound like your speakers go lower with greater bass power.  You don't "listen" to the subs.  You listen to extended power response as if it's coming directly from your main speakers. I have two Vandersteen 2wq subs. which have adjustable level and "Q".  So you can adjust the relative tautness of the subwoofer response.  I recently traded in my Vandersteen 3A Signatures for Treo CTs.  One of the first things I had to do to properly mate my two subwoofers with the Treos was to decrease their output level as the 3A's sensitivity was 89 db and the Treos 85 db.  Just last evening I further tweaked that output level so the system is congruent.

If you are just looking for more bass, then there are much more affordable paths to follow.  In the end, it depends on why you want the subs.

A big +1 to Hifiman5 comment. 

I recently put together a system for my kitchen and decided on a Hsu VTF-1 MK II to go with a Cambridge cxa80, Schitt Gungnir multibit and Scansonic MB-1s. Because of not being able to do a straightforward placement of all components flexibility was going to be key. The options on the Hsu made fairly quick work without a lot of sub crawling and if it weren't a big black cube would be as invisible as its well blended sound. I'm impressed as hell for the $450 it cost. 

@hifiman5 thanks for the detailed post hifiman5. one quick question, wouldnt the current on the speakers drop if you connect subs to them in parallel? because current would decrease for parallely connected components right?