I've used the face to face, out of phase blanket method, very effective. Present speakers make that pretty much impossible, so I've just listened through break in, unless something seriously off break in shouldn't be that difficult. Most noticeable thing I hear during break in of all components and parts substitutions, and I do a lot of the parts substitution thing, is a certain sense of what I'd call 'up tightness'. Excess of attack, lack of sustain or decay, and veiled quality. Over time as things begin to loosen up I hear this sensation of 'blooming', an opening up or relaxing of presentation, this may also include larger sound stage and more dimensional imaging. Sometimes this blooming can be sudden thing, one minute up tight and very next the blooming begins, quite an amazing thing when this happens. Really is very educating to listen through entire burn in. Still, I don't bother with listening through burn in with any component or part prior to amplifier, you can do this silently with signal flowing from source.
Also, I certainly concur with those who believe burn in applies to our ear/brain complex. We ourselves need time to adjust to sometimes very subtle changes in sound quality, over time we develop comfort zone for present sound qualities, changing things brings back analytical mode so we may be overly critical or 'uptight'.