Here is another product that claims to convert regular audio signals to fiber optic and enable you to install an after market radio in the e89 without having to replace the amp.
I imagine it does the same thing that the harness I bought from Germany does.
I find the OEM BMW amp to be pretty darn good, but then my other car is a Fiat Chrysler Ghibli with stock audio, and it sounds like crap whenever I play anything but talk radio.