0to60in4

Has anyone upgraded the audio system in a 2017 S550 Cabriolet or any variant of A217? Mine has the standard Bermeister audio system. I would like to find most efficient way to obtain low-level full-range audio signal to add aftermarket amplifiers and speakers. Ideally I would like to obtain audio signal from fiberoptic BEFORE audio signal is processed by stock amplifier. Otherwise I plan to use Audio Control DM-810 to accept high-levels from all processed channels at stock amplifier output to sum together and RTA to flat response low-level audio signal.

If anyone has done audio upgrades in this vehicle (A217), where did you install subwoofer inside the cabin (not in truck)? Also does anyone have details about stock speaker sizes and amplifier locations in the vehicle?

Thanks