I have Boston Z6 speakers installed in my doors. The tweeter can be mounted separately or with the mid/woofer. In my install the front tweeters are in the original location and in the rear doors a hole was cut out to the front of the interior door handle. The Z6's easily fit in the doors.
The sound is incredible. The Z6 tweeters are the same used by Boston in their high end home speakers.
I was in Philly for Thanksgiving. Could have given you a demo!