First, open your soundalias' csv file. I recommend opening it with a spreadsheet app first so that you can find the correct CSV column quickly. After you find what you're looking for, open the CSV with Notepad++ or similar. If you have Microsoft Excel, you can edit it directly from the program. When you're done, just hit CTRL+S or File -> Save. Confirm with "Yes" that you want to keep the existing file format.
You need to change the "bus" that the sound plays on. Typically I see people using ambience, weapon, or full_vol - these are fine for weapon sounds or other SFX, but you should not be using these for music.
Find the bus setting in your soundalias and change it to
Then rebuild the FF that you have included your sound in. Now you should be able to control the volume of the music in-game by using the Music volume slider in the Sound section of the World at War pause menu.