Which is better for a DBA (Swarm); powered subs or unpowered?

Hi cheeg, 
let me relay my subwoofer experience to you and a recommendation to use your $1K wisely. 

I have successfully and seamlessly tuned subwoofers in my car and home systems.  
I started out with one decent sub at home and it worked really well and two worked slightly better and was very successful. 
If you want the best bang for your dollar (2) Rythmik L12 ($559 each, shipped) will sound excellent.  Someone I know has this setup and it is impressive in a high end 2-channel setup. 
Second best would be (2) SVS SB1000 subs.  

Start by placing them just to the outside of each speaker slightly away from the corner and back wall. you can adjust position once you have broken them in.  

"tune" one sub at a time- tune the right sub to your system noting the best crossover that blends and doesn't cause any peaks or notes that are too loud.  Then adjust the phase by "timing" it to your main speakers.  Play some repetitive bass beats and adjust the phase for the most focused, most powerful notes.  Adjust level to blend.  
With the first sub playing (as a system) add the second sub to the "system" and repeat the steps for crossover, phase and level.  
Now run with this for several weeks and adjust only the level of each sub.   Take notes and write down all of your settings and when you make adjustments in the future.  
After that the subs will be worn in and likely sound louder and slightly different.  Adjust as needed to make the sound smooth.  
This has worked very well for me.  
peace and good luck 

1. I've never tested anyone who could not localize a 30Hz tone playing from one channel or another.

2. The reason low frequencies are summed is for stereo playback to keep the stylus in the groove.

3. Nope. If the bass is mono, it still bears a time relationship to the rest of the spectrum

4. Sound is sound and behaves the same across all frequencies. Waves don't collide. They pass right through one another. We may hear or measure a null, but that is a mechanical artifact. Move away from the null and the signal level returns to the same level.

5. If our brains summed and averaged, we would not be able to perceive low end at all.

6. never read that. Please supply a reference. Not by DBA advocate, s'il vous plait.

7. 200ms!?!?!? Surely you jest. That's almost a ¼ note @  120BPM.    Again, please supply a reference.

8. Again waves don't collide. They get absorbed.

There’s also no performance, imaging or quality concerns dependent on the direct bass sound waves from any specific, or combination of subs, arriving at the listener’ ears first.

If that were the case, one could place a sub anywhere in a room and hear no difference.

Subs are not brick wall devices. They output significant energy well into the mid-bass. If they are not coherent with the mains, they smear the impulse response.

Perhaps DBA work with time incoherent mains where everything is a huge bucket of mush and when crossed over below where there is any significant program, but with time coherent mains and crossed over much above 40Hz, they never can.

LOL - so many opinions, so little consistency!  It would be interesting to test out these hypotheses using 3 subs, at different distances from the listener, set up so 2 of the subs together have the same volume as the third one alone.  Run the same mono source to all three, and use an A/B switch to flip between the single and the pair.  Anybody want to bet on the outcome?  (hint; I don't think any 2 people on this site would agree)

PS: for the comparison above, no signals over 100 Hz need apply.