subwoofer advice

Snapsnap, if I understand correctly, you want to power your passive subs with the amplifiers which are already in your active subs, is that right?  

If so, that's extremely unlikely to be feasible.  The amps in your active subs are matched to the impedance of their woofer, and adding a second woofer in parallel will probably cause your amp to shut down.  And adding that second woofer in series will probably cut your amplifier's power in half.   

I suggest powering your two passive subs with an amplifier dedicated just to them.     

Duke

Snapsnap wrote:  "I will have to do some research on what amp would be suitable for subwoofer duty, and how many are required to drive multiple passive subs."   

I use the Dayton Audio SA-1000 for the Swarm.   Assuming your passive subs are 4 ohms each, the SA-1000 would put out almost 500 watts into the 8 ohm load of your two subs in series.  If your subs are 8 ohms each, you can connect them in parallel for a 4 ohm load, into which the SA-1000 puts out a little less than a kilowatt.  

Snapsnap:  "On that point, will the additional amp(s) be connected to the main amp or to the preamp?"   

It depends on what kind of inputs the subwoofer amp has.  You can find subwoofer amps with either and with both.   

Duke