Who knows how to set up a bass swarm? (DBA)

What do you mean? African or European?

Yes they will be better with more subs. The deal is you keep whatever bass comes out of the main speakers and add to it with subs. You do not want to do a crossover to eliminate low bass going to the stereo pair. You want them to get all the low bass they can because the whole idea of DBA is multiple bass sources energize the room more evenly. Therefore if your main pair are full range that's great keep them full range that's two more low bass sources. 

Locating the other subs with a DBA is extremely flexible and forgiving. In fact its recommended they be located asymmetrically. That is, different distances from the mains, the corners, and each other. In my room for example two are along the left wall, two are along the right wall, and a 5th is on the front wall near the left front corner. They are all different distances from their respective corners. 

With your current 2 subs I would try them like that, different distances from the corner. Whichever corner, it hardly matters, and you can try different locations. It seems to me that the more subs the less fussy they are with location. That may be why with 5 it hardly seems to matter where mine are. With just 2 subs right now it might make more difference, you will just have to try and see. 

I would set crossover first, then level. When you get close to the right level be very careful to make very tiny adjustments. If you're not sure if you even changed it that's probably about right. Play a lot of different music at different levels. Take your time. The ear is very sensitive to low bass once it reaches a certain threshold at which point very small changes seem much bigger relatively speaking. Finally when you are really close you can tweak phase, which is really very similar to moving them around. I had a hard time noticing much difference and with me, once I get to that point I figure I'm done. 

Edit: I see that millercarbon posted while I was typing... oh well, hopefully this won’t muddy the waters too much...

I’d suggest placing one of the REL subs along one of the side walls, closer to the back of the room than to the front, but not the same distance from its nearest corner as either of your mains.

Place the other REL sub along the back wall, closer to the other other corner, and again not the same distance from its corner as either of the other three.

If you have the option of inverting the polarity on the REL sub that is farthest from the mains (phase = 180 degrees), I suggest doing so.

For subs which are closer to your ears than the main speakers, I suggest not running them up any higher than 80 Hz, and less than that if the lowpass filter in those subs is less than 24 dB per octave. What you want to avoid is, the subs passing upper bass/lower midrange energy loud enough for give away their locations. Since they are closer to your ears than the main speakers, you ear/brain system will tend to hear them as the source of these sounds, which is why we want to roll off their top end aggressively.

If you are doing this by ear, here’s what I suggest:

First adjust the level (loudness) of your subs for best sound. You want them all at approximately the same loudness, so that all are approximately equal contributors. How loud the subs are makes the biggest difference, so we do that first.

Next adjust the low-pass filter frequencies of the subs. This makes the next biggest difference.

If you have phase controls, adjust them last. This makes the smallest difference.

Now cycle back through this sequence several times. In particular, setting the level may take a long time because the ear is especially sensitive to small changes in sound pressure level in the bass region.

Best of luck! 

Duke