Bob,
Sorry ....not laughing at you but the plots that Ethan shows have huge differences over a few inches in a real listening environment. It has to make one "laugh" and put things in proper perspective when one looks at a Stereophile set of pristine measurements! What are we actually getting at home - even the best of us - and how much 'processing' is the brain doing to compensate for these peaks and troughs.
Certainly Ethan's arguments seem to support the contention that a device that produces modest amounts of additional even harmonic distortion may very much help improve the sound in a typical room with nasty suckouts. As in the case of nasty suckout at a particular fundamental, it will be all the other harmonics that still allow our ears/brain to interprete, fill-in and hear the note with a fundamental that actually isn't there...perhaps this is why even harmonic distortion is often pleasing and adds warmth and detail that we could not appreciate before in our less than adequate surroundings...