@soix I think @audioguy85 is referring to adding separate sub-woofers to speakers, but not to those that are already part of the speaker system. Not only Wilson, but Vandersteens Quatro have built-in sub-woofers. Those are fine. He is questioning the wisdom of adding sub-woofers by end-users which are not part of the speaker manufacturers recommendation. This is just a trial-and-error procedure hoping to get something in addition to what main speakers deliver.
Why I'm not adding a sub to my 2-way monitors for music
I've updated my blog post with more data, more analysis and the conclusion that in my particular case I do not need a subwoofer. I encourage everyone who is on the fence about adding a subwoofer or not to read and comment. I think that either way you'll be able to make more informed buying and configuration choices.
Everyone's situation is different but I hope the post helps you get to the right conclusions.