Here's the story I usually relate when threads of this nature pop up:
I bought my DAT M6 from my local Diamond dealer as I wanted the three year warranty.
When I bought it I asked this very same question of the manager of the shop and by way of response he asked me for my keys.
He then walked out to my car with a DMM in hand and popped the trunk. Using a test-tone CD out of his own ride he set the gain on my monoblock to where he wanted it then proceeded to hook up the M6 in its enclosure to my bass amp.
With that same test tone CD he cranked the volume on my deck to around 29/35, listened to it for about 15 seconds, and then said something to the effect of "Yeah, sounds alright to me," and then took his CD out of my HU and went back inside. (bear in mind that this would be the guy in charge of handling a warranty replacement if his treatment of the product he had just sold me proved detrimental to the driver)
At least to me that little display completely negated the age-old myth that subwoofers require a certain break-in period prior to wanging on them as hard as you can.
As already stated by helotaxi the sub(s) you're using will loosen up with use and begin to sound different/louder/whatever after being used for awhile but there is no necessity to "take it easy" on them right out of the box. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif