Since the CMU can take a while to come back to life after turning your car off, and then tapping the ignition switch once for Accessory (ACC) mode, many of us miss the feature that many vehicles have where the audio will continue playing after stopping your engine, at least until you open your door or a programmed period of time has gone by. Sergey (ssh16) has reported discovering that by holding the button on your Automatic shift lever while shutting down your 124 Spider with your left hand – kind of an awkward maneuver, you’ll actually be in ACC mode rather than in OFF mode, allowing your radio to continue playing.
Apparently stopping the engine while in Neutral rather than Park will also produce the same result and is probably the maneuver to remember when you wish to remain in the vehicle and continue listening to your radio/streaming audio, and simply slipping it into Park afterwards. This gives you up to 25 minutes more time before the CMU turns itself off, but this can be extended by tapping the brake pedal once prior to that timeout, for another 25 minutes.
If you have a manual transmission, there seems to be no solution other than hitting the stop button twice while in neutral and your foot off both the clutch and brake pedal. If done quickly enough, you’ll end up in ACC mode with no interruption in radio play.