analog to digital

Solution
You will need to connect a bluetooth transmitter to the receiver.
If it has preamp or record outputs you can connect it there. If not then you will need a speaker to line level adapter like this one
http://www.crutchfield.com/p_142LOC80/Scosche-LOC80.html
If the speakers are not a stereo pair you will get mono from each and if you want to use more than one will need a BT transmitter that will pair with more than one device like this one
http://www.avantree.com/product-bluetooth-audio-transmitter-avantree-priva-1031.html
You will need to connect a bluetooth transmitter to the receiver.
If it has preamp or record outputs you can connect it there. If not then you will need a speaker to line level adapter like this one
http://www.crutchfield.com/p_142LOC80/Scosche-LOC80.html
If the speakers are not a stereo pair you will get mono from each and if you want to use more than one will need a BT transmitter that will pair with more than one device like this one
http://www.avantree.com/product-bluetooth-audio-transmitter-avantree-priva-1031.html
 
Solution