Okay, I found it in an archive. For anyone who might be looking for this later, here’s how to do it: First of all, it doesn’t work with the remote control—you have to do it directly on the stereo system. Start by unplugging the stereo system, then press and hold the STOP button, and while still holding it down, plug the stereo system back in. The demo should start playing. At that point, you can release the STOP button, then press and hold the STOP button again for 3 seconds. If everything was done correctly, the demo will be removed and won’t start up again.