Sub Question. One higher quality sub or two lesser quality? (Rythmik vs HSU)

      Yes, I use the Dayton SA-1000, that Duke mentioned, in my AK Debra 4-sub DBA.  It's been on virtually 24/7 in my system for over 5 yrs now and still is performing flawlessly. 
     A good option is to buy one of these for $300-400 from Parts Express or Monoprice and build or buy 4 passive 4 ohm subs and create your own custom swarm. The Dayton also functions as a sort of sub control unit since it has controls for volume, crossover frequency and phase along with l+r ch line level inputs and A+B sets of speaker outputs.  Its 1,000 watt class AB amp has plenty of power to drive four 4 ohm subs and its controls allows for the setting of all four subs together as a group.
   Another method many use is the MiniDSP,  which has a single set of analog L+R line level inputs and up to 4 L+R analog line level outputs to connect up to 4 self-amplified subs.  This unit also has settings for volume, crossover frequency and phase plus the capacity to customize the crossover filter slopes.
    There's many ways to skin a cat.  No matter how you do it, however, the cat can be relied upon to protest vehemently and loudly.

I've never skinned a cat as far as you guys know,
Tim

I see two speaker outputs on the Dayton. How does that work to drive 4 subs?

2 on each wired in series?

mapman:
" I see two speaker outputs on the Dayton.  How does that work to drive 4 subs?

Hello mapman,

     It's actually 2 pairs of speaker outputs on the Dayton sub amp.  I have a front pair of subs connected to the top pair of outputs and the other pair of subs connected to the bottom pair of outputs.
     The connection method of the AK Swarm and Debra systems' subs are also a bit unique as all 4 subs are connected in series/parallel  configuration.

Tim 
    

As I read it the two outputs are already in parallel and connecting two subs to each directly would result in 4 in parallel which would could result in loads 2 ohms or less with nominal 8 ohm subs. Two in series to each would seem like a better idea?

Cornwalls are super efficient, so what Brian said makes sense.  I've never felt like they tried to upsell me when I've talked to them.  Did he make a recommendation for your situation?  I'd reach out to the guys at SVS and see what they suggest also.