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

Yes...and I started to give a one word answer.
I recently designed a Home Theater Room for an old friend.
Everything done as well as I know how to do it.
So, dry wall with OSB glued and screwed non consecutive seams...Golden Ratio 'shaped' room.
Incorporated were a pair, (two, not one) JL Fathom Subs.
The blend is marvelous.
They are fast, faster, fastest...and very smooth.
Typically I have never been a fan of trying to blend subs...but let's get real here.
What floor standing speaker has sub/bass response? Not many.
The JL's are just about perfect to my ear...and when you play a 20Hz, sweep to about 200Hz, there's this incredibly smooth blend that just makes you smile.
I chose two, not just because he could afford it, but because regardless of what some say, bass is not 'non directional', just 'less directional' and the two gave me great in room 'balance'.

Good luck.

Larry

Larry, I completely agree with you on bass being somewhat directional. If I had to go back to using a sub I would buy two and set them next to the speakers aimed at the listening position. In my car the sub is behind the seat and crossed over at 60hz. I can clearly tell were the bass is coming from.

If you place one sub in the same plane as the main speakers you can't tell where the sub is, assuming a 60Hz 12db/octave crossover. If you place the sub closer or farther from the listening position than the mains you may have to adjust the arrival time (which is tricky stuff).

Bass sounds are omni-directional, but in a car the shock waves through the structure of a car aren't, and that's why you can tell where the sub is. Even in a house I can tell that the bass is coming from somewhere in front of me, but I can't discern the sub's position between the speakers. Or even that it exists.

Still, I have to agree, two subs are better than one, and optimum positioning seems to be one near each main, assuming that's a good position considering room modes. (It often isn't.)

Bass may be omnidirectional but that doesn't mean you can't localize the source. I think that would be called "omnipresent". Like when my wife spots an audio purchase on our credit card online statement within minutes or hours of a new transaction.

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.