The crossover you are talking about is unnecessary and with your speakers actually counterproductive. The advantage of multiple subs is primarily from having multiple locations for bass. Adding four subs adds four new low bass locations. Crossing over from your mains removes two locations. This is what we call "own goal".
I’ve gone the whole route from none to one to four to now 5 subs. Was expecting you to have read myself, or Tim (noble100) or audiokinesis or perhaps even Toole or one of the white papers on subs. These would all say what I am saying.
The number of subs is so much more important than anything else that it frees you up to do four pretty much any way you want. The least expensive will be what I did, buy 4 cabs and drivers from Parts-express.com and drive them with one or two Dayton SA-1000 sub amps. The Dayton has all the flexibility you want and with four 10" drivers will get excellent DBA for well under $3k, possibly under $2k if you catch a deal and paint instead of laminate. Mine are genuine Rosewood veneer and 2 amps (really only need one) and I was still under $3k. https://systems.audiogon.com/systems/8367
You could also get excellent results with a couple of the Tekton 4-10 subs. Or any combination of powered and active subs. That is one of the beautiful things about taking this approach, it is incredibly flexible and effective almost regardless of how you go about it.
I’ve gone the whole route from none to one to four to now 5 subs. Was expecting you to have read myself, or Tim (noble100) or audiokinesis or perhaps even Toole or one of the white papers on subs. These would all say what I am saying.
The number of subs is so much more important than anything else that it frees you up to do four pretty much any way you want. The least expensive will be what I did, buy 4 cabs and drivers from Parts-express.com and drive them with one or two Dayton SA-1000 sub amps. The Dayton has all the flexibility you want and with four 10" drivers will get excellent DBA for well under $3k, possibly under $2k if you catch a deal and paint instead of laminate. Mine are genuine Rosewood veneer and 2 amps (really only need one) and I was still under $3k. https://systems.audiogon.com/systems/8367
You could also get excellent results with a couple of the Tekton 4-10 subs. Or any combination of powered and active subs. That is one of the beautiful things about taking this approach, it is incredibly flexible and effective almost regardless of how you go about it.