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'. 
128x128cheeg
@audiokinesis 

"My recollection is that Toole was referring to a Harmon subwoofer integrator processor which optimized the gain, frequency response, lowpass filter, phase, delay, and equalization based on in-room measurements. I assume it does what they claim."  

Duke, thanks for the answer. I think Toole was referring to an integrator, but I don't know it was the integrator process. On chapter 13 "Making (bass) waves - below the transition frequency" he shows several examples where 4 subs are used in a rectangular room and optimized (through an optimizator) to minimize seat to seat SPL variation at 5 seating positions. The optimizator adjusts overall level (dB), delay (ms), and EQ at a given point (frequency, Q, level). It's not clear to me if said delay was introduced through DSP or just a "phase" adjustment.

I can measure with REW and optimize with MSO for example, but if actual delays are needed then I would need a digital processor to incorporate these.