It's a bit of a stretch from a technical point of view, but I suppose I'd concede that the surround materials on a woofer and midrange driver might "loosen up" with some well-recorded bass from complex dance, orchestral, or jazz CDs.
Set the level fairly loud--as loud as you might listen from day to day, but not a deafening level--and play the aforementioned discs for a few hours. DO NOT load up a CD changer with a bunch of CDs cut at different levels (as most discs are), crank up the volume, and go away leaving your system blasting away. A friend of mine (who should have known better) did this and went off to his job. He came home to find smoke rising from each of his $6000 pair of speakers and the amp, amazingly, still working but almost on fire!
In most cases, I believe that what actually is being broken in is your own set of ears, not the speakers. Your ear/brain acoustical system is learning to accommodate and accept the sound and tonal signature of a new pair of sound reproducers that you're not yet used to.
I've never seen a set of technical measurements before and after speaker "break-in" that showed a particle of difference in measured performance. But hey, barring the aforementioned blunder by my friend, you can't hurt anything.
Hope you love the sound of your new Axioms!
Axiom Resident Expert