Good post by nowave. There is absolutely a lot of perception of break-in, as admitted by Sushi. Hence my comment that almost everyone who hears break-in hears a similar set of effects: relaxing treble, maybe extended bass response. This is not a coincidence, nor would I chalk it ALL up to the power of suggestion, advertising, or exaggeration.
Chess, you said that Alan had controlled experiments which led to "empirical proof based on the science, not conjecture. It has been tested. It has been proved." First of all, Alan did not test for break-in, as I understand it. That was not his goal or design. Alan has compared many loudspeakers using controlled experiments, and he simply commented that his results did not indicate changing loudspeaker characteristics. As I said, these tests spanned hundreds of hours, which would mean that the vast majority of the tests were performed on broken-in speakers. Did he specifically examine the first few tests performed, and compare them to much later results? I don't know.
In any case, it's impossible to definitively prove that NO break-in ever occurs. It's infinitely easier to prove individual speakers DO exhibit break-in, at least subjectively, and maybe to a lesser degree, quantitatively. And while the Axiom crew has taken measurements to test for break-in, this does not magically overturn decades of empirical evidence for all other speakers and listeners. Not to mention the fact that some speaker companies probably explicitly engineer for it. So the true burden of proof is MUCH heavier on the skeptic's side, though I have no problem if you say "I never heard break-in on my speakers." Just allow me the contrary privilege.
Biwiring? Never heard it. I really have no idea, and in Stereophile I don't think they claim it's any silver bullet. Expensive cables? Better materials and construction often do sound better, but there are diminishing returns, as with anything in audio. I think you just have to keep your expenditures proportionate: cabling should be somewhere around 10% the system cost. Biamping is great, but expensive. Just as having extra power in your amp helps the dynamics, having a separate amp for tweeter, midrange, etc. will also make it easier to drive.
Sushi: how do you meausure the eneven performance of a tweeter when given a large burst of power, as opposed to a steady tone? The driver motion is so miniscule that I absolutely think there's room for things we don't yet know how to measure.