If you *must* keep the oem audio setup then you need to find a working DSP amplifier that's compatible with the build date of your car. Check on realoem for the amplifier part number and any other's which are compatible. Then keep searching ebay, craigslist, bmw forum classifieds for a DSP amplifier with part numbers that are compatible. If you find one/some, then you need to purchase and get them delivered to you and then connect up. Assuming the one you buy is indeed working, you then need to hope it continues to keep working as the module you get is likely to be around 15-16 years old!