My R58 Coupe has the base radio. No tweeters in the A-pillar for me. So I decided to skip the A-pillar w/tweeter purchase as they are $150 each. Found the tweeter I installed at parts-express.com. Nice aluminum mounting ring that matches the factory chrome rings a little bit. Not a big fan of chrome but since its already in there I just matched it the best I could. I've done installs with the tweeter in the door before and the outcome was pretty good. Crossovers are key. Electronic crossovers are awesome but passive will suffice for now. Some pics if your interested.

 

Looks great! I'd be interested in a how-to on removing the door panels. I've got a resonance rattle in one and I keep thinking about lining it with some sort of deadener. Do you have any pics of that process?

 

This should help.