I would think that integration is a separate issue. And in most rooms , best most linear and smooth (in term of frequency response bass) is obtained with multiple low frequency radiators/subwoofers.
I disagree with the "stereo" in bass below 80 Hz,. I have a subwoofer in front and another in the back side of my listening room ... about 1 meter behind the listening position, a couch. I can't hear it. People that were invited in my room including, golden-eared audiophile don't hear it either, i know it is anecdotal.. The scientific reality remains that the directional clues come from frequencies well above 100 Hz.
The answer is the one provided by
@sweetchaos
Based on that the JTR Speakers Captivator 4000ULF-LP, is the Ultimate Subwoofer for any sane person with room space, it is the Gold Standard.
Peace.