Best option would connect the Bluetooth transmitter to the tape record output on the amp.
If you don't have one then preout or a speaker to line level adapter like this
http://www.crutchfield.com/p_142LOC80/Scosche-LOC80.html
could be used to feed the transmitter. The downside to this is that the volume control of the amp would affect the level feeding the transmitter. This would allow you to send all the sources connected to the amp to the BT speakers.
If you only want to send CD then you can split the output of the CD player and connect it to both the amp and the transmitter.