Forgot to try it again. I wonder if it works.
I was listening using the fm transmitter in the dock, and out of curiosity, I plugged my headphones into the line-in jack, just to see if the audio turned off, and it did not. Maybe you need to remove the stilletto from the dock. I'll try it if I ever remember to bring my mp3 player in.
I've used it and it really isn't anything special. It won't go through the SL-100 or use the FM transmitter.
Basically if you plug something into the line in jack, and have your Stiletto base plugged into yoru stereo, whatever you have in the line in will "loop" through the dock and to your stereo. Turn the Stiletto on and you get the Stiletto sound.