2013 mb sl 550, stir+, and interface

Guys: Need some help here... as usual. I've got a 2013 MB SL550 that I'm installing a Beltronics STiR+ detector system. In order to keep the install low key, I'm using the Mid City Engineering Cluster Interface (Part # 9500HS125/500) for the control and display of the STiR+. That's relatively straight forward... except for the audio mute connections. I need to connect the STiR+ system into the car's audio control system, so it can mute the telephone, or the stereo, or whatever else is on. That's the need... my problem is the "where" (there's a steering wheel "mute" control, but I suspect that's not the place to start... unless I really know what I'm doing...). If anyone has any suggestions, pictures, or whatever, that will point me into the correct direction, I shall be eternally grateful... Thanks, Chris

Why not try the steering wheel mute wire? You might actually know what you are doing. I mean it makes sense that if a mute is needed and MB located it on the SW controls that it would work as a mute.I can not explain to you what "nothing" is in a scientific way. What makes matters worse is you won't notice it when you finally have the opportunity to experience it.