Watch out when downloading media for fpsc as there could be a licence problem.
By law you are duty bound to ensure that the media is protected encased in one big exe.
Fpsc however creates files with the exe and if your soundfiles can be accessed for copy or use then you have infringed the copyright and licence.
I create audio, music etc and at the moment I am unable to put any of this in the store because of this very issue.
Copyright and licence do not just require you to pay for the privilege of using the said material but also to protect the material as far as possible.
I know it's a downer but it's the same rules that will protect any game you make.
I can only surmise that anyone already selling sounds in the game store has waved their right for you to protect their intellectual propery but check the licence to make sure.
If still in doubt ask fpsc where you stand
mpc