That’s the same unit that I had in my CLS.
There’s a way of connecting an aux-in cable. It involves soldering a socket with two wires to a circuit board (instructions are easily found on the internet), then you’ll need a CD with a recording of silence. The idea is that your CD player is triggering the system but the source signal is coming in via the aux-in socket.
My local audio repair man soldered the wires for me for £20. I tried doing it myself but it’s too fiddly. Once done, I had crystal clear sound and could play music and radio from my phone.