Hi guys,
So after upgrade CIC for my E60 530i, I have the same problem like other people with Hifi Sound system, without bass and very bad sound.

I know the cause, but I am looking for the best most efficient way of solving.
1. Ask and buy Technic harness with Ms8. But I don't want to use aftermaket amp.
2. My thing: So can I replace Hifi OEM amp to Logic7 OEM amp ( many used on Ebay) ? but I am wondering:
- What problem after I replace Logic 7 OEM amp with not enough 13 Speakers ?. If I turn off logic 7, sound system will work like normal ?
- Connector 20 pin to OEM Hifi and Logic 7 is the same, but need I re-wire or only plug and play.

Other question:
- I have extra 4 OEM Speakers (Font left,right. Real left, right) because upgrade 4 BSW speakers. Can I use them for Coax center speaker ?.

- Have we any way to add rear door speakers without cut the door ?.

Thank you so much for help.