Cheap Sub

I use an old Marantz reciever from the 70s to drive a dual voice coil passive sub. Even 30 watts/ch is enough to drive a 90db sub to get down to 25 Hz or so. Easier to fine tune the sound to integrate it into the rest of your system as well. Just don't forget your low pass, maybe spend good$$ on your chokes as everything else will be transitory.