For in-car listening, it's not always more drivers = better. Unlike at home where you have a large room, your car is a small enclosed space while driving. This means there's more to it than just adding drivers. For example, those rear speakers might in fact reduce what you hear from your subwoofer. How? By nulling some of the waves of your subwoofer/midbass.

*D3nB3r

Break-in is a subjective matter. Some believe in it, some doesn't, some are in the middle. But as a matter of fact, most speakers are already partially "broken-in" at their manufacturing factory during quality control testing. If you don't believe me, try Youtubing how the likes of Dynaudio or Focal-JMLab manufacturing process.

At the end of the day, breaking in is true because you can quantify the changes of the speaker due to a softened suspension, etc. However, it won't make your speakers sound from crap to great - that's a myth so that installers may dissuade buyers from returning their product.