MAJOR UPDATE!
rewritten code, redesigned interface, and much more instructions.
Current Problem:
you have to close the program to restart, kill the app to restart, before trying next setting.

Download Server Program From Here (installed on PC)!
(download the zip file in "download" folder, unzip it, and run server program)
(install java runtime before you run "BluetoothAmplifierServer.jar")

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you can get source code from here.
https://github.com/getabyte/Bluetooth-Amplifier-Server
https://github.com/getabyte/Bluetooth-Amplifier-Client
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recently I discovered this app, might be useful.

https://www.rogueamoeba.com/airfoil/