C:\Users\YOUR_USERNAME_HERE\AppData\Roaming\boomboxstable
And on macOS it is:
/Users/YOUR_USERNAME_HERE/Library/Application Support/boomboxstable
C:\Program Files\Common Files\Adobe\CEP\extensions\com.mtmograph.boombox
C:\Program Files(x86)\Common Files\Adobe\CEP\extensions\com.mtmograph.boombox
C:\Users\YOUR_USERNAME_HERE\AppData\Roaming\Adobe\CEP\extensions\com.mtmograph.boombox
/Users/YOUR_USERNAME_HERE/Library/Application Support/Adobe/CEP/extensions/com.mtmograph.boombox
~/Library/Application Support/Adobe/CEP/extensions/com.mtmograph.boombox