I also hacked its CTIA inline remote and created an IR gateway so that I can leave the player on a stand and at least have play/pause/skip-back/skip-forward support using an old spare sony IR remote. the trick is to use a TRRS cable and send the control signal in over the inner ring and gnd.
and, in fact, it does not seem to be ctia (not resistor programmed) but its something else - a click-based protocol. 1,2 or 3 clicks to perform those functions. I found that completely by accident, btw and it has not been documented anywhere that I've found.
so, I'll bring that along, too, since it was a fun and somewhat useful little hack.