Good question Leo. As someone reading all sorts of strange and not-so-strange claims floating around on audio forums, I've struggled with questions like these as well.
My initial opinions, formed of my skeptical nature and electrical engineering training, were that a lot of these claims were pretty much bogus. Really now, I stayed awake through, and did well in, solid state physics (and, IMO, that's not a feat to scoff at, either...). And never did I hear anything about transistors, resistors, and god forbid wire, "burning in". For capacitors...well, maybe over time the dielectric can build up some residual charge, but that would simply decrease their overall capacity, which for many applications would make them worse, not better. Now granted, eventually changes do occur, but as an engineer I call it "wearing out", and it's not supposed to be happening in the first few hours... In fact, since tolerances are achieved and tested for at the factory, logic (and my textbooks) would indicate that the best a circuit (and notice the word here....I'm
not talking about moving parts that need lubrication, like a car engine or speaker diaphragm) will perform is when new. Over time, hopefully a lot of time, a circuit will degrade, as dielectrics break down, or thermal stress affects tolerances, or hysteresis affects affects transformers, etc.
Anyway, that was my initial take, but I know the feeling you're having. The more you read about people being able to hear differences, the more you wonder. The most insidious part of this is wondering if maybe your hearing just isn't up to snuff. This in turn causes the
desire to hear these differences, leading in some cases to the death of objectivity.
Now, I am certainly not going to claim that there are no differences. Not only would that potentially start a flame war, but it would just be my opinion, and no more or less useful than anyone else's opinion to the contrary. You're going to have to decide for yourself. Before you read too much, though, and just "go with the flow", here's a link to an interesting piece that deals with marketing-speak and why you should be wary of certain claims:
http://www.sundial.net/~rogerr/truth.htm
(Check out the sections "A revolutionary new speaker system" and "truth and superstition in audio").
More to the point of your original question, though, I noticed you followed up with some quotes weighing in on the subject, including, *gasp*, some words written by a marketing department. Critical reading and thinking skills are a must, because one could easily quote plenty of contradictory opinions on this topic and plenty of others. For example, check out "The Burn-in Lie" section in this pdf document:
http://www.audioperfectionist.com/PD...watchdog10.pdf
In actuality, this section is written by someone trying to "debunk the debunking" of burn-in. However, when I read the passage, my own internal BS detector goes off far more on the rebuttal than the original quote he's trying to argue against. Note how the author of the rebuttal first simply attacks with useless generalities ("He'd have to be deaf to believe this drivel"), and then proceeds to "prove" the original author wrong by talking about the speaker case (specifically excluded from the original author's assertions), and about how warm circuits perform differently than cold ones (a fact that is easily provable with elementary thermo / solid state calculations, and has nothing to do with a "burn in" period). Anyway, enough from me, as I stated before, you should read critically and form your own opinion.
The most difficult thing about all of these opinions about what does and does not matter in audio is this: many, many people (well....not in the population at large, but in the population that posts on these types of forums) believe they can hear these differences. This seems to force someone reading these opinions to either of two conclusions: a) they really CAN hear a difference, or b) most people are liars.
I certainly can't accept option b...it just doesn't make any kind of sense (remember, opinions are free, but the equipment people buy isn't!). That seems to leave one with only a single choice. However, that's not necessarily the case. There's a third option. Namely, that most people
truly believe that they can hear a difference. And, while there is a lot of debate on what differences truly are audible, and to what degree, there is a fair degree of consensus in psychology that people really do believe that they can perceive differences, when, in fact, testing shows that they can't. Note, again, in the first link in this post, under the section "Good amplifiers can sound the same". The author expresses a sentiment commonly found in double-blind testing, that they will swear, up and down, that they can hear differences between types of gear. Then, in the same exact environment, they score just around 50% right as soon as the testing goes "blind".
Combine this with the fact that distinguishing differences before and after a break-in period requires a) a long (days?) period between listenings and b) no ability to toggle back and forth between before and after states, and.....well.....you form your own opinion.
-Nadim