You can take matters into your own hands, just to be clear. iTunes? Or whatever other music media you'd use. Don't need to rely on SE for something so simple.

Isn't there an option to adjust the music volume? I've never actually looked for that, so I'm not sure. If not, I can see it being a bit of a problem trying to hear the sound effects and such if you'd have to just mute it so you can hear your own music. Still an option though.

If the file keeping is similar to FFXI, you can swap out files for your own customization, albeit in XI, there were some limitations.