[KDN]

and you can put another copy in Sounds subfolder, put the briefSound command in the .mis file and hear it in the mission briefing screen

[MAIN]
briefSound samples/Sounds/Vera_Lynn-The_white_cliffs_of_Dover.wav
MAP Net6Island/load.ini
TIME 8.0
CloudType 2
CloudHeight 1500.0
army 2
playerNum 0
[Wing]
RZ_NN00
...

Just for good measure make sure all you .wav file do not have any spaces in their names.