Sorry my mistake. No sound.cfg, only a sound.ini file in the Captain_Sim\757-III folder, no sound.cfg (or a sound.ini) file in the Captain_Sim\757-III\sound folder. So not both, only the sound.ini file is needed.

Have you checked in the SimObjects\Airplanes\CS_B777-200ER-II_GE90B\sound folder (or any other CS 777-II sound folder), because there is a sound.cfg in them. All but that one I mentioned redirect the sound to the CS_B777-200ER-II_GE90B\sound folder which has all of the necessary .wav files in it.