Help with wiring of stereo jack
Maybe mix bass and treble feeds together using a couple of 22 ohm resistors - you'll need to likely cut down the volume anyway to avoid sonic injury when using headphones and the 2 x 22R resistor will help. You'll need to do both channels. If you can supply the exact pin-out on the bluetooth board I'll scribble over it for you. Without the right details it's guesswork and could definitely be pants\$^1\$ if incorrectly wired. If the outputs are bridged this may be a problem but not a showstopper. It depends on you and your willingness to use small audio transformers or experiment a little bit.

\$^1\$ http://www.urbandictionary.com/define.php?term=pants