Hey Shaggy,
You might want to get some double-side tape and experiment with tweeter placement before you do this. I had a 320i back in the day, that was used by a local audio shop as a demo vehicle. Tweeter placement for proper sound stage is critical in a car enviroment as you're already sitting closer to one side. High frequency is
very directional. We found if you aim the tweeters across the car at the head on the opposite side, it widened the soundstage and improved the seperation. In the vents gave us more of a left and right seat bias. Firing them into the windshield made them harsh, I uninstall the Boston FX3's and went back to the stock speakers in my 300. Those stock 3 1/2's are better that you would think if you roll them off at around 5000 hz and pass the high freq on to a good tweeter! I'm experimenting with some MB Quarts tweeters now. As of now the ideal placement seem to be either mounted on the pillars by the windshield cross fired or surface mounted on top of the stock grills angled for cross-fire.
Most people can just replace the stock dash speakers with some of the 3 1/2" 2way's on the market and be perfectly happy.
QUALITY sub-base is easy in this car. ONE JL Audio 10w6 will fill the cabin with solid, undistorted base notes without eating up trunk space !
I'm at an age in my life where quality of sound is more important that alot of distorted volume
Stop by one of your
BETTER local car audio shops and ask them for some suggestions.
Don't commit till you experiment !