I found this post
It describes that all E9X have three main levels of audio system, plus another only found in the E92 M3,
Speaker provisions - Mids with Tweeters in the front door
Base audio - Mids in the front and back with 2 x 6.5" under seat Subs
HiFi or Premium system - Mids with Tweeters front and back with 2 x 6.5" under seat subs.
However none of the above describe the setup in my E92, I only have 2 mids in the front and 2 mids in the rear... Anyone have any explanation? Is it possible for me to add Subs under the seats and add tweeters to the mids up front (even one or the other) without having to get an amp. Would the wiring exists in the vehicle... Does my vehicle even have an OEM amp... Please help