DEBRA / SWARM DSP?

I have a miniDSP 2x4HD on my 4 sub array with the same amplifiers (thanks so much Duke!).  As MC states, you'll be limited to one set of DSP settings per amplifier.  Perhaps not ideal, but in the end you're really correcting for 1 listening position, not 4 subwoofers. 

The miniDSP paired with REW and a calibrated microphone (e.g., the umik-1) is really a wonderful tool.  Make the measurements at the listening position and immediately import directly into miniDSP to create the appropriate filter.  *Many* more options and flexibility than the onboard EQ settings on the Dayton, and if you're set up correctly, you can make all the changes directly from your listening position.  I find that invaluable for evaluation accuracy.  So much easier than getting up, moving a tiny knob without feedback, and then sitting back down and trying to figure out how the sound changed.  

I have two sets of outputs on my pre-amp. One goes to my main amps, the other to the minidsp. One minidsp output then goes to a dayton with two 8-ohm subs connected in series (front and left). The other does the same, but runs the right and rear subs. 

Inside minidsp 2x4 hd you have the options to combine the stereo inputs into a mono signal, control the crossover cutoff and slope, input up to eight (if I remember correctly) eq adjustments, control volume level (up to +2db), and adjust delay. All of that can be modified independently for each input and output channel. It's a truly amazing piece of equipment.

My only complaint is that the minidsp (and the Dayton amps) have a low input impedance (8 kohms I think) and can be difficult for some preamps to drive.  If you've got a tube preamp with output capacitors, you'll want to be careful they're big enough not to start rolling off the output to the subwoofer system.

Note that using a y-cable will present the same issue. Consider checking with your pre manufacturer to ensure your unit can drive both the sub system and your main amplifiers.

My Don Sachs pre could, but my new dht pre (one single tube of voltage gain) just doesn't have enough current to push both.