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

How loud do you like to listen? Do you listen to a lot of rock and want gut thumping low end or do you prefer classical or jazz and are looking to just fill in the bottom end?

With powered subs you need proximity to AC and you will need interconnects, unless your subs have wireless calability. If you are using RCA connectors and have some long runs over 10' to 15' that could be an issue. If your system is balanced then long IC runs should be fine. With passive subs you will need speaker cable and if you require big power and a long run then you may need to use heavier gauge wire up to 12 awg maybe even 10 awg.

If you like it loud, a good powered sub will offer better speaker protection. With passive subs and a separate amp you will more than likely get none, so if you hard clip your amp it will probably be re-cone city. The rule of thumb (at least it use to be) is to use an amp that is capable of twice the output power of the speakers maximum handling capacity. So if your subs can handle 200 watts @8ohms then you want an amp that can deliver 400 watts @8ohms and so on.

With powered subs you will have more individual control, which for some will be a good thing and for others not so much. A dba system itself makes integrating easier but as the room gets larger control becomes more important. It will be dependent on how sensitive you are to time domaine issues. You should be fine either way with your room.

Some subs (I think REL is one) allow you to wire them in a way that reduces the burden on the main amp to cover frequencies below a set cutoff, like 80Hz. Does anyone know if that is possible with the Dayton?

Almost all powered subs and I believe this is also true of the Dayton amp, only come equipped with a low pass filter, which allows you to set the frequency cutoff point of the signal that is sent to the subs.  You would need an actual crossover to do reduce the burden on your main amp. 

is it advisable to use all the same brand/model of subs in the swarm, or does it not matter?

There is not a lot of detail when you get below 80hz so in my opinion the subs do not need to match. I use three different brands of subs in my 4 sub dba with no issues.

what is REW? 

I believe REW is a type or brand of room analysis software.

Is it possible to run 4 passive subs off of one amplifier, say like a Crown XLS series? 

Yes as long it has enough power and can drive the impedance load that the speakers are presenting. The load will vary depending upon how the cabinets are interconnected.

Thanks for all the new responses! Let's see if I have this right:

@ieales doesn't like Dayton subs b/c they have "no delay so there is time smearing. What you end up with is a fat, detail-less low end pillow."

@b_limo seems to agree with @ieales, at least to the extent that "with the dayton amp, you aren’t able to adjust [the phase of] each one independent from the other", which is needed if the subs aren't equally spaced from the listening position. Makes sense.

@clearthink also seems to agree with @ieales, unless the listener likes loud, thumping bass (I do not, unless I'm wasted and listening to loud, poorly produced classic rock (which does happen, but not as often as I'd like).

@audiorusty seems to lean toward powered subs over one bass amp, because they have more individual control. But he cautions that DBAs are more easy to integrate, since you only have one amp to adjust. My response would be that I don't enjoy spending time tweaking my speaker settings, but if that's what I need to do to get what I consider to be "good sound", I will put up with it. Score one for powered subs. (since you asked, my taste is generally 60's-70's folk, prog rock and classic rock at moderate volume (85-90 dB) for enjoyment, and classical at lower volume for background while working or going to sleep (but I still want it to sound clean). Not so much jazz.

@heaudio has a LOT of good info regarding the difference between getting the time delays right vs getting the phase right, and I have sooooo many questions. He seems to think you can get this right with a well implemented DBA, but I'm not sure how. If he has time to discuss it more, I'd love to know how to text him (or email, phone, whatever).

@millercarbon initially gave some very useful input, and seems to recommend Dayton(s) in a DBA, but my last round of questions scared him away and he has moved on. Nevertheless, I thank him again for all his advice.

So, after all these responses, I have a lot better understanding of the issues, but am no closer to deciding whether I should buy a Dayton and cheap passives, or buy two better quality actives and save my pennies for 2 more.  Maybe the answer is "it doesn't matter", but I really hate that answer... Thanks for hearing me out.  Peace, and enjoy the music!