FWIW, I went from a single sub (REL) & am very happy with my pair of 4-10's. Big improvement in bass (as expected) but also soundstage. I've never tried 4 2-10's though... So there is that.
Tekton 4-10 Subwoofer
Looks like there is a new Sub from Tekton. It looks cool! Eric Alexander, if you are out there, would love to know more about this new product.
https://www.tektondesign.com/4-10-sub.html
https://www.tektondesign.com/4-10-sub.html