Your soloution may well require some custom wiring.

On the early cars (pre 2002 ish) the front speakers are indeed dual coil, and that is why your BT audio does not work.

You have the option of adding a small speaker in the panel above the driver's knee, next to the gong, then wiring it in to the TELNF signals.

Also you can get a later NG radio post 09 2002 and add the TELNF pins in to the sockets on the back. You will also need an updated FM amp (eBay) and possible a 17 pin to 40 pin adaptor.


EDIT: I saw in your post on E46 fanatics that the car is a 2004. This means you may not need to buy much in the way of radios, amps and adaptors, you just need to wire the TELNF signals into the empty pins on the stereo.

Post some pictures of the back of the stereo, and have a look in the 12 or 10 pin connectors for two black/white and black/brown wires in a twisted pair on pins 6 and 7 of X18805 or 3 & 8 on X13321.