Hey, thanks for the patch! The new commands seem to work fine, although it does look like the BGS takes a full 2 seconds to load when entering the range for the first time, which results in the BGS to pop it at a much higher volume instead of fading in gently (which it does if you leave the range and re-enter)
This seems to happen with regular SE too. I did try and use the regular play BGS event command to make sure it's not the file that's too big and has loading delay, and they all played pretty much instantly, so it looks like the proximity sound plugin somehow delays it. I would appreciate it if you could look into that as well!
(This also happens in your demo project btw, making it impossible to sync up the hammer sound with the sprite hitting the anvil.)
I recorded some footage of the issue too: