This is meant to be an amplifier module that can be mounted back to back on the KRC-86B Bluetooth module.
The power is supplied by a 12-18V source of about 1.5-2A, that can either be a AC/DC power supply or a battery.
The PCB has the same demintions as the Bluetooth module and has a 5V supply for that module build onto it.
Even though the module is mean for mono use, it can easily be modified to a stereo setup. All that is needed is another module where R6 is removed on the left channel and R5 is removed on the right channel, together with U2 on one of the modules.
All parts for this project can be found on Ebay, and all resistors, capacitors and ferrite-beads is 0603 while the output inductors is 10mm x 10mm in size.