Breaking In New Speakers...

Use'em. Just don't expect much for the first couple of weeks. Don't sit in the listening chair expecting to hear something wonderful right away. Unless you are dealing with a deadline regarding a return option, just relax.

The biggest change will happen over the first 24 hours of play even though they will typically smooth out even more as time goes on. There are some easy methods for breaking in pairs (out of phase, placed face to face, and covered with a heavy blanket) but I don't know how you could acomplish something similar with that crew that you've got coming.

Put them face to face, a few inches apart. Wire one out of phase. If you have a test/break in CD, put it on repeat for a few days. Volume should be a little loud, but not enough to get you evicted. 100 hours or so will do the trick. This will drive small animals insane...

It will take a while to get accustomed to the new sound but they should break in relatively quickly - a few minutes of hard driving music will generally do it for the suspension (spiders can be stiff initially) and perhaps a few hours for the cap in the crossover (may or may not be audible depending on quality and design). After a few hours most of the change should be your acclimitazion to the new way your music collection sound (you have to update your sonic memory and this takes the longest time).

Mofimadness's description is the way to go. I just want to add that you also need to feed the speakers with mono signal. The out-of-phase connection will cause bass to cancel each other but not the higher frequency. You can cover both speakers in a heavy blanket to mute that. Now you can break in your new speakers without driving small animals insane.