Yours didn't come with the other adapter that has the mini usb + headphone usb splitter ? Thats what I use for mine in car to charge and have audio. As i hacked a spare set of the stock headsets into a aux out cable for my Pioneer headunit. Just cut the buds off and soldered wires to the speaker cables after the mic so I can still use it for in car calls. Works like a charm.
Here is the guide i followed to connect the headset speaker wires to my head unit in case any of you have a pioneer head unit with a cd-changer port and want to do this yourselves.
http://stereophonik.com/gutterslide/IP-BUS_Hack/
Works great to lsten to music thru mort player ether from my sd card or stations from shoutcast. I just turn the pre amp down a bit so the mort player music is lower then the rest of the audio that way my gps software can be heard over the music.