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

I want to start building a swarm (starting with 2 subs), on a budget.  Starting with $1000, am I better off buying two used powered subs, three less expensive used powered subs, or a subwoofer amp (eg Dayton SA1000) and two (less expensive) used unpowered subs?  What is the advantage of having a discrete subwoofer amp?  Room size is 13'x22'. 
You probably would be better off with powered subs IMHO. The second hand market is a good place to start. You can get a used Martin Logan Grotto i for less than $500 on EBay. If one amp goes bad in a powered Swarm, you don’t have to shut down the whole system to get it fixed. Use wireless transmission to daisy chain them and you would be able to move them around without the limitation of a cord. Get familiar with REW to be able to set them up properly and sky is your limit. 
Ha!, Very nice spinaker01. I hope advice from a fellow member of the 4-sub DBA Club (AK Debra system) will suffice for cheeg, instead.
My opinion is that 2 subs will sound and perform about twice as well as 1 sub and 4 subs in a DBA configuration will perform about twice as well as 2.subs. I first heard this opinion from the owner of Audio Kinesis, Duke Lejeune, but I’ve verified it’s accuracy via my own experiences in my own system and 21’x14’ room.
You’ll clearly notice the advantages of using multiple subs beginning with the use of 2 properly positioned subs and these advantages have been proven to be optimized in virtually any room and with any pair of main speakers with the use of 4 properly positioned subs. The advantages you’ll clearly notice are the bass being faster, smoother, more powerful and dynamic, more detailed and better integrated with your main speakers. The main difference between using 4 subs rather than 2 subs is that 4 subs will provide improved bass performance throughout the entire room while 2 subs will restrict this improved bass performance to a single designated listening position or seat. You’ll also notice the bass improves in its speed, smoothness, power and dynamics, detail, sense of effortlessness and integration with your main speakers as you move from using 2 subs to using 4.
No matter how many subs you choose to initially or eventually use, it’s very important you have controls to adjust the following: a regular Volume control for level, a Crossover Frequency for adjusting the frequency below which the subs become active and a Continuously Variable Phase control for fine tuning the sub‘s phase from completely in-phase to inverted phase and all points inbetween. If you use self-amplified subs, all 3 of these controls are required and need to be set on each sub individually. If you use a Dayton SA1000 sub amp/control unit with 2-4 passive (not self-amplified) subs, all 3 controls are set once on the Dayton SA1000 sub amp/control unit for all connected subs as a group.
If budget is a concern, I suggest you start by buying the DaytonSA1000 sub amp/control unit and 2 either used passive subs or 2 new passive subs from Parts Express or Monoprice. If you’re handy, you could save even more $ by building your own subs with kits or individual parts from Parts Express, Monoprice or any other source.
I just recommend you choose subs of reasonable size and weight, with a minimum of 10” drivers, rated bass extension down to at least 20 Hz and 4 ohm impedance if you can. Remember, 2 properly positioned subs will provide very good bass at your designated listening position only, but not throughout your entire room. However, it’s also possible, in some rooms, that 3 properly positioned subs will perform as well as 4 With very good bass throughout your entire room.
There’s also a unique wiring method you need to use for best results called series/parallel which I can detail later if you decide to go with this option.
Another option is to use wireless self-amplified subs such as Syzygy or another brand. I also know the SVS SB-1000 self-amplified subs are very good subs at a great price of $500/each which could work very well for you as either a pair or a swarm.

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