Before selling my old Peugeot 206, I removed my Kenwood stereo and I put back original Peugeot radio, model: Clarion PU-2325A(B). Bad news was that the radio was now locked and demanded a 4 digit unlock code. I could not find this code in any of the paperwork that came with the car so resorted to the Internet and Google...

Read more: Finding Peugeot (Clarion) stereo unlock code

I'm not an audiophile, but standard BMW stereo system sounds pretty bad to my ears. There are obviously very fancy (and expensive) audio system upgrades possible, but I decided to go with an official BMW Alpine kit. Mainly for two reasons: 1 - sound quality is considerably better than standard stereo (I'm not really interested in window shattering bass, etc). 2 - everything is plug and play and reversible - no modifications, splicing, wire cutting.

Car:

• BMW 320 (E90) Sedan
• Manufactured October 2011
• BMW Professional Stereo

Standard BMW Professional Stereo consists of:

• BMW Professional Head Unit
• 2 x front door speakers - 4'' (10cm), 4OHM
• 2 x under-seat subwoofers - 4OHM, not sure about size
• 2 x rear deck speakers - 4'' (10cm), 4OHM

Required parts:

• BMW Alpine Upgrade Kit (BMW part: 65412163268) - £360
• Door surround trim left (BMW part: 51337171201) - £25
• Door surround trim right (BMW part: 51337171202) - £25
• After the upgrade is completed, the Head Unit may require re-coding to "flatten" the built-in equalizer. BMW charges around £130 for this. In my experience BMW dealers were quite confused about this and gave me conflicting information whether the re-coding was required and why... At the end they did the "re-coding" for around £90, but I'm not convinced that it was required (or made any difference).  

Read more: Installing BMW Alpine Stereo upgrade (BMW 3 series E90)