No harm will come just playing them as-is and enjoying the different phases of the break in, but to spare the family from excessive noise, I used to lay flat faced speakers face down on a thick carpeted floor and play bass heavy music. You’re basically loosening up the surround and spider suspension of the woofers during break-in. Bass should be the most impacted component of the music spectrum until things loosen up, but if there’s a mid-bass driver that can benefit from some flexing over time also. Low frequencies and higher volume (within reason) will cause those drivers to move the greatest distance, which is really what helps the suspension loosen up fastest. That first few hours should make the biggest difference.
Depending on the caps used in the crossover there could be some notable changes in the upper mids and treble too.
