This is a video showing a stereo upgrade to my 2002 4.4 X5. I replaced the factory head unit with a double DIN touchscreen HU and replaced the DSP amp with a 2 channel amp. I removed the front speakers and installed two-way coaxials and lastly removed the factory subwoofer and installed a DIY sub box with 10″ driver and amp.
I skipped quite a few steps as there is plenty of information on the web and youtube. For reference, you may want to look at the following pages if you’re doing an install from scratch.
These videos show how to run wires from the dash to the trunk:
Wiring diagram for E53 DSP speakers:
Door removal for speaker access:
DIY subwoofer box dimensions (change 13.5cm dimension to 11cm for better fit):