To those of you who continue time and time again to proclaim the tired "full range speakers don't need subs" mantra (or any variation of it) the above comment illuminates why it makes no difference if your mains are "flat" down to 30, 25, or 20 Hz (or even subsonic, for that matter). Their balls will still get clamped by the pliers of simple physics. You can only fight back with physics and that's what distributed bass does.
And to understand that distributed bass is a system in and of itself, not custom tailored to any specific set of main speakers, is also in critical in understanding its intended purpose. My DB rig works with any mains I set up and the only adjustment I have to make to the subs when switching main speakers is the gain on the plate amps (since sensitivity of main speakers and the way they interact with the room is almost always different).