Get two subwoofers, one will drive you nuts. If you are using a larger driver in a properly designed sealed enclosure servo is not necessary. The larger the driver the lower the distortion because the larger driver does not have to move as far staying within the linear range of its suspension. This assumes drivers of equal quality. In a two subwoofer system 12" is OK, 15" is ideal as is 4 12" drivers. What you do need is a powerful amp with DSP control. Check this out https://www.parts-express.com/dayton-audio-15-ultimax-subwoofer-and-cabinet-bundle--300-7097 Then you install one of these https://www.parts-express.com/dayton-audio-spa1200dsp-1200w-subwoofer-amplifier-with-dsp--300-8000 and there you have it. Two 15" DSP controlled subwoofers for $2000.00. Spend just a little more and get the 2400 watt amp. These kits go together beautifully. If you are not good at putting on a finish you can cover them in black carpet or take them to a cabinet refinisher who can lacquer them black. Parts Express sells black carpet with an adhesive back. This is a very serious subwoofer. The driver is first class and significantly better than the ones you mentioned. The amp is no joke either although I would save a little more and go for the 2400 watt version.
The future belongs to the brave so, get out that Gorilla glue and have at it:)
The future belongs to the brave so, get out that Gorilla glue and have at it:)