Forgive me here tom, but I'm not sure I'm understanding why you're needing to do this.
I'm assuming you already have a bluetooth dongle to get the music from your PC to your bluetooth headset? And are you connecting your MP3 player to the PC with something like a 3.5mm jack to RCA Phono X 2 (male)?
What I'm thinking is it seems a lot of trouble to go to in order to play the radio from your MP3 player through to your headset.
I might be barking up the wrong tree here, but why not use a first rate streaming radio player like
WinAmp. As long as it gets the radio station/s you want, it's IMHO one of the most stable (signal wise) web radios available with really good quality sound.
There's also
Screamer radio player, but in my own experience, it balks on a lot of radio stations WinAmp plays effortlessly.
Anyways, if I'm off the mark with what you're after tom, give it to me with both barrels, and I'll come up with something better.

I play my full size MiniDisk player through my PC to copy off some tracks I only have on MiniDisk, and I use the Jack-RCA connecter mentioned above for this and the music comes straight through to my headphones without any need for any extra software. I also have XP Home.
I've just had a thought that it might be a slow internet connection pushing you into the MP3 player solution.