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.
535d LCI, Xenon Adaptive Headlights, ACC 2 (Stop and Go), Lane Departure Warning
Retrofits M5 heated/lumbar/memory and active backrest adjustment seats, rear heated and folding g seats, SAT Shifter, paddles (SA2TB), HUD, Rear blinds, Electric steering column, SA430 Folding and EC Mirrors, High Beam Assist, CIC, COMBOX Telematics, DVB-T TV, JBL MS-8, JL HD900/5 + HD600/4, Morel HO II, Morel Integra XO, JL 12W6v2 and Jehnert in Audio.