You're in luck
I just helped my buddy design a system for his 2009 323. I have about five years of experience selling car audio, and have designed and installed many systems over the years. My specialty is budget systems.
The audio set-up in the 323 is the base 'Stereo' system (as opposed to the HiFi or Logic 7). It uses 2 x 4" speakers in the doors (mid range paper cones with rubber surrounds- no tweeter), 2 x 4" speakers in the rear deck (same as fronts), and 2 x 6.5" subs (yes I said sub) under the front seats.
Unlike many BMW systems with an external amp, all 6 speakers run off of the deck, including the subs.
I didn't feel like taking the responsibility for hacking up a new leased 323, so we farmed out the labour to East Hamilton Radio, who did a decent job with the install. Here is what we did for his car, which addressed the awful sound of the stock system.
1- Installed 4 channel Alpine amp with variable x-overs (front doors on HP and underseat subs on LP). Alpine MRP-F300, which comes with a high-level input (also known as speaker level input); $250
2- Installed 2 x 4" Hertz EP4 speakers in front doors; $200
We left the subs as is for now and the system sounds pretty fantastic- it's a little bright up front for my taste, but my friend LOVES it. When my friend took the car in, EHR's installers spent a good hour arguing with us that the car had an external amp, and then trying to find it. They didn't, as it does not have one, but be aware that fishing for free advice from car audio shops may yield incorrect guidance. They are used to the 328i's system which DOES have an external amp (with built-in x-overs) and tweets in the doors. Your car, like the Euro 320, does NOT have a factory amp.
The next phase in the upgrade would be to swap out the 6.5" subs under seat (which use an inverted magnet structure in a shallow plastic box) for Earthquake SWS-8s. We haven't done this yet, as the additional power from the amp really did a lot to clean up the sub's bass.
PM me with questions.
SOLD- Now Enjoying Honda Civic
Last edited by bigfeller; 07-02-2009 at 08:03 AM.