I upgraded my speakers sometime back and did lot of research on this.

All the speakers in E70 (doors and dash) are component speakers, which means there is a 4" driver and a tweeter. This speaker size is actually uncommon and not many car audio manufacturers make these speakers.

I am not sure about the size of the subwoofer. I have actually retained them and they are connected to the stock amp. My aftermarket subwoofer is connected to an aftermarket amplifier. So technically, I have 3 subwoofers.