Thanks for the info!
Being as I am not an audiophile, I am going to go with the box. My installer has been around a long time and does tons of custom work, etc, etc. I have used them for quite a while and trust them. They said they have done a few in the E90 3-series (same fitment) and said it sounds very good. I was skeptical on the rear firing nature of the box, but he assured me that it would sound very good, etc, etc. So i figure, wtf, I will give it a shot. If I don't like it, I will sell it on Craigslist or something. lol. I figure I am getting a great amp, so I could always change the speakers and box later if needed...but i am pretty confident it will be a good fit, for what i am looking for.
FYI, here is a link to thier website. They don some pretty kickass stuff. http://www.acmetopsandtunes.com/audio.html