Thanks for your post, I have been searching through the web and except of your note I have found just one unconfirmed message on pinouts.ru...
As you seem succeeded with the stereo headphones adapter I would like to kindly ask you for some help with the same.
My only intention is getting the stereo sound to my headphones from the device and I do not care about the microphone nor play/pause/mute functionalities at all (your confirmed "Stereo audio" option).
So far, I got couple of 4-pole 2.5mm plugs and experimented with them. The problem is that I am getting no signal on pin 3 and getting mono signal (left + right channels together) on pin 2 (do not believe all the connectors are bad). Have you ever met with something similar?
The source mp3 is in stereo so, this is not the problem.
Thanks a lot in advance; any help/idea is appreciated.