Picked up a free Makita DMR107 which still sounds pretty good but only has radio/aux functions
Added Bluetooth for extra versatility
Removed AUX2 board and wired up audio wires to BT board purchased for <$4
5v power was picked up from one of the 2 ICs onboard

Step 1: Locate 5v Power

Solder 2 wires from ICs
Pin 4 = gnd
Pin 8 = 5v

..To bluetooth module power in

Step 2: Connect Audio to BT Module

I cut wires to AUX2 and soldered these to BT module audio in
Cut the red wire to allow AUX2 to be selected
Hot glued module to inside of top of case to get best BT reception

Unit has been working great with no pops/clicks etc