Start reading this here http://www.e90post.com/forums/showthread.php?t=641323
That sticky will answer all the questions you asked, I know it did for me when I first started to learn about our cars stereo.
Originally Posted by Balln2k12
I'm so frustrated trying to find the correct solution to upgrade my system. Have read multiple threads, but seems there are a lot of missing parts of the puzzle to make a simple purchase.
I have 2010 with iDrive but with base system. I know I can purchase BSW system, but don't want to drop $700 for 2 pairs of speakers.
I need to know the following:
Window seals (with tweeters): what is the correct part number from BMW?
Speaker wire adapters: Technics kit? How do I purchase a kit to allow me to upgrade all my speakers without cutting/splicing the factory wires?
Battery thermal connector: what adapter can I use/purchase to hook an amp to the battery?
Under seat subwoofer bracket: I see that there is an adapter needed to install 8" woofers under seat, and I see there is also a speaker wire adapter needed.
Component speaker options: what brands, models work in front door and rear deck for best fit and good sound?
Subwoofer options for under seats?
JBL processor? I have seen photos of people using one, why do I need one and other options?
If I can get all the right information to do the correct job, I would be more than happy to put together an extremely detailed "turnkey" install help guide for others.
Thank you all so much for the help