Please see /t/9889/1 on MP3tag on Mac OS.
If the app-way is not sufficient as it causes problems with the external drive you have to look for a different way: either copy the files onto the internal volume or use a different emulator.
I can tell you only the conventions as expected by a native windows program. You have to make sure that these standards are met on your system. How to do that? I cannot look over your shoulder and cannot see what options you have.