hi great to see someone doin a proper job for a change. I am currently builidng my install which is total custom high end sq usiing hertz mille speaker. I have built many BMW's which can be seen on my web which is urrently being updated. I would advise you to cut the metal just to allow he speaker to breathe into the door this will give you a nec enclosure and good mid bass response but you will have to protect the speaker from water ingress and moisture. I normally install a moisture guard and add some dyanamat type product to enhance the sound futher. I noticed you have gone stock location for the tweeters too ! As well as this you could have kept your factory amp just unplugged it like you have done and installed a Audio control LC8 or a JL Audio clean sweep would have been better as this automatically sums your speaker inupts gives you remote turn on and preputs to your amps ! Any q's pm me love to help ! Will be posting pics of my install progress...as i run a business my own car gets left behind !
BMW ACS Individual