Best and OEM way to do this will be to go down the combox route and use mobridge L7 kit. Combox can be coded to read data (easily upto 320Kbps or higher if phone/file supports it) digitally and it goes over the USB to combox and combox will send it on most (fibre so lossless) to CIC and CIC will route it again on most to L7 mobridge.
This only makes sense if you have CIC and if you have apetite for combox.
Just an alternate thought, this keeps your signal digital up until the last point which is input to ms-8.
650i F12 - HUD, 6WA, SLI, Logic 7, Dynamic and Adaptive Drive, Comfort Access, Soft-close, top-view,
Previous X5 40d M Sports and 535d LCI