Sharing audio upgrade on my non-DSP in '99 528iT. Kept OEM headunit/cassette (for looks mostly). Replaced stock speakers with Bavsounds & replaced OEM CD changer with GROM bluetooth which punches above its
BMW 540i 5 SERIES E39 DOOR SPEAKER NOKIA SET REAR RIGHT + LEFT 01-03 OEM | eBay
BMW E39 5-series Top HIFI Front Door Speaker 65138369069 for sale online | eBay