Are the JL Fathom subs really that good....

Yes they are very very good and very fast.
There is no problem integrating them into a 2 channel system, it just takes time and more of it if you are using 2.

I bought one f113 and it took me close to 10 weeks to fine-tune the position, cross0ver points and phase (plus break-in) and all I can say is these are the fastest and best subs I've yet owned. Prior to this I had 2 REL Stentors and had issues with reliability but these JL's seem to be built like a battleship!
(Dealer disclaimer - not for JL at this time)

Bizango1, if bass is omnidirectional, and that's a physical fact below 100Hz, then by definition you can only localize a source by means other than listening. :-)

Bass is a funny phenomenon because you feel it as much as you hear it. Your sense of touch does not work like your ears. Hearing is logarithmic. It takes a doubling of power to produce a small difference in apparent loudness levels (3db), yet as everyone knows a doubling of mechanical force feels like a doubling of mechanical force. So a 3db increase in sound level at 40Hz can result in a feeling that you've really turned up the bass, because you're feeling it.

Regarding JL subs for 2ch audio, the only thing that kept me out of an F212 was that it didn't have a high-pass filter for the woofers on the mains. All of my demos of various subs I did revealed that unless you use a high-pass filter, preferably at about 60-80Hz, the bass sounded muddy and over-blown. Yes, I know this is a highly controversial point. Some folks like that bass-heavy sound, but not me. I looked into a Bryston 10B-SUB to perform bass management, but F212 + 10B-SUB = big bucks. I just got a Velodyne DD18+ instead. A pair of SVS SB13-Pluses are also a good choice for music, and include high-pass filters.

it's all about the set-up interface and taking the time to do it right. if the set-up software is not up to snuff, the resulting sound will also be sub-par. same applies to taking your time and getting it set-up right (to your liking).

can't comment on JL but it took many weeks working with my velodyne dd12 to get it right....it is truly seamless.

two things i discovered during the journey (for my set-up)

1)much better sound running good mains without a cut-off. this allowed me to back off heavily on the sub volume while still adding the right amount of slam way down low (below 50)

2)there is no single best configuration for all music types. i set-up 4 different audio profiles and depending on the music, a specific sub set-up really makes a difference (rock vs r&b vs classic ect..)

if you do it right...a good sub can really make a positive, seamless difference.

Irv, I would say that most often integration problems between the main speakers and subwoofers are not caused by the fact that the two are not time aligned. For example, if we place a subwoofer between the speakers and then we move it say 2 meter away from the plane of the two speakers, then at the listening position we will have a time delay of approximately 6 milliseconds between the frequencies emitted by the woofer and by the speakers. As far as I know, most experiments show that the brain considers all frequencies detected within a 50 milliseconds window as par of the same direct sound, i.e. it will detect no echo (repetition of the same sound) for such small intervals. Consequently, I would that this is a second order effect.

On the other hand, destructive and constructive interference (which creates bass nulls and/or significantly reinforce some specific frequencies) cause much more significant problems. Since this depends entirely on the room dimensions and position of the speakers and subwoofer(s) in the room, I would say this is by far the most important complication one faces when trying to integrated a subwoofer into a stereo system.

Regarding two subwoofers vs. one subwoofers issue, two subwoofers yield a more even response in the room (i.e. less null or reinforcements). Most often one can get just as good results with only one subwoofer but this requires very careful set up (this is not two say that dialing in two subwoofer is a piece of cake - not by a long shot).