Hi JaimeG,
Actually, the sound of the M60ti's won't change: "break-in" is rather a red herring. What you are really "breaking in" is your own set of ears, accommodating new speakers with a different spectral balance with different dispersion traits.
If you find the M60ti too analytical or "bright", call Joe Vassallo, our service manager, on the toll-free line and ask him to mail you a set of resistors that simply clip onto the lead to the tweeter. There is a 1.4 ohm value and a larger one. The former reduces the tweeter output by a dB or two; the latter attenuates the output even more. He will tell you how to pop out the tweeter and clip on the resistors.It's easy to do and no soldering is needed. I don't use the resistors on my M22ti's but I do use a set on the M80ti.
Regards,
