Very fair question and I wish I had an answer! The MB Quart speakers I installed have a ring attached to the 5.25" driver making the mount size 6.5". Why they didn't go with a 6.5" driver is something Bavarian Soundworks would have to answer and I'll bet they have avery good reason.

After having the speakers for a few days they are growing on me. The low end is loosing up and the speakers break in. The MB Quart set is very capable of making bad sources sound bad! You'll find that radio stations (or especially Sirius) that sounded OK with the OEM speakers can now sound really lousy. But it's the source that's bad.

It really is amazing how poor the OEM tweeters are.

I still have one door to go...