Acoustic treatment

Has anyone ever tried having a single big sub and a few more smaller ones?  I'd think a single sub that goes to 20hz would be enough and then 3 smaller ones that only maybe go down to 30hz could be used to even out the response.  Locate the big one in the best spot for very deep bass and the other three can even out the response from 30-80hz.  There tends to be a huge price difference between subs that will go to 20hz vs 30.  

The reason I ask about adding smaller subs to a big one is that I, like a lot of people I'm sure, already have one big expensive sub.  I would never buy three more like it.  I measured the response with the Behringer ultracurve and measurement mic, and equalized out the worst of the problems.  I'm not unhappy with it how it is but if I could add a few smaller, cheaper subs and get a dramatic improvement I might consider it.  

Deeply discounted subs are common.  For example, I could get three KEF Q400s for about a grand.  It's a sealed box like my current sub so I'd expect them to blend fairly easily.  Adding three more drivers would allow me to let the big sub take it easier.  The question is whether adding fairly cheap subs would solve more problems than it causes.  Would they start audibly distorting if I turn the volume up a bit or would the fact that there are three of them plus the big one allow for more clean dynamic range than I have now?  Maybe I'd leave them off if I want to listen loud and only use them to create really high quality bass when I'm listening at moderate volumes.