For those that care, I finally got it working, but it seems it doesn't like .ogg files.
Essentially, you need to put the schemes folder (which you can find in the other download provided on the site) in the BMS Debug folder, and then you put your BMS songs here: Library/Application Support/Aquanbeats/Contents/BMS/MainBMS/
I haven't been able to get the folders organized but it definitely works if you just drop the songs there. |