It isn't clear what you want to do. Do you want to use your headphones with the MP3 player directly? Well that's not going to work. USB headphones are for use only with computers and other devices with generalized USB outputs. I see plenty of adapters to allow an audio/video interface with a computer but not something that would allow USB headphones to connect to an MP3 player, etc. What I can't fathom is why USB headphones don't plug into the electronics with a standard 1/8" stereo plug (or more if there are more drivers in the headset) so the phones could be used with whatever you have. Perhaps there is such, but I've never looked. To me, it seems stupid to make them any other way - I know I certainly wouldn't buy any made any other way.
.bh.