Gamekeeper was kind enough to let me upload two zip packages with a total of 74 music files at the download section of
http://airwarfare.com/sow/index.php
The files are of the era or with WWII theme and are ready to be used as soon as you extract them. I currently have ALL 74 files in the Users "music" folder and they play in random and continuously in the main screen and most submenus screens. If you would like to do that, back up and DELETE the two music files from the Main (not user) "music" folder.
Out of curiosity I left the main screen on for about two hours and it played 21 from those files with ONLY three repetitions!!
Currently, the FMB does not read .ogg files but the name of the file can be input manually. I have managed to get a file playing in the PLAYER briefing in Quick Mission and Single mission environment but only if you don't customize that mission. It looks that you can have sound files attached to all short of briefing sections and a few playing type options too.
I am looking forward when the connection of sound files to the mission briefings is fully activated.