What follows is all my personal opinion...

I think that just because one uses multiple microphones for EQ it does not mean that it changes the characteristics between one sitting position and the next. To me, this method seems designed only to produce a pretty curve. Unless a listener's ears are 5 feet apart, he will never get to hear the sound as it was sampled. It may be a good measure of the overall characteristics of a room (dead, bright, etc.) but, IMHO, not of the listening experience.

I don't have any experience with multiple mic setup but to me it seems like letting the air out of three tires to fix a flat.

I would just buy another sub instead of spending $800+ on microphones. I agree with lanion, I think it is better to take a couple of samples at two or three positions and tweak. If one position is drastically different than another, we might need to apply some sound treatment or adjust the sub's settings (or move the microphones closer together - I am kidding on that one).