speaker break in volume level

Just turn on a radio station at medium level while at work and let it do its thing, no drunk listening levels needed.

My recommendations are to break-in the speakers as you are going to listen to them. Higher volume levels with dynamic music will help loosen up the surrounds much quicker.
I go with whatever my ears can handle.

Since they are monitors put them face to face and a couple inches apart and wire one of the speakers out of phase (right to the left; left to the right connection on the back); then throw a heavy quilt over the speakers to deaden the noise for the neighbors and crank them up with dynamic CD on replay or a radio station with dynamic music. Give at least 4 to 5 days and they should be ready for critical listening.

I believe the volume level equates to the specific speaker. My Zu Definitions, though I listen at "normal" volume, (acutally very low, late at night and early in the 'morn) required very high volume levels for a very long time for break in. This was suggested by all who owned them and the Zuboys, as well. Other speakers I have owned I broke in at moderate volume levels--a tad louder than I would normally listen. Leave your rig on when you go to work (if your house is vacant during the day) if the loudness is a bother when you're home. Even if you're leaving the house for a couple of hours let it rock. This saves your tympanics.

Break in means that the response drifts over time. Any cone material or surround material that is unstable over time, in a manner enough to effect audible sound, is probably not such a great choice of material for a speaker.

If it drifts after several 100 hours of play.....what will the sound be like after several thousand or tens of thousands of hours played. In all likelihood, at some point, the speaker will have drifted away from its intended or factory calibrated response.

Cars used to require a careful drive in period and not because they were great cars; it was a manufacturing quality problem and tolerances were poor and surfaces had a higher wear during break in. Eventually this has been solved with higher quality manufacturing techniques.