Your log show that's something is not entirely right with your audio drivers, but it also said it managed to find an audio device too. If there was a problem with the audio engine, NO sounds from GSX would work, but you said you have *some* sounds.
Does the sounds change if you are inside or outside the airplane and if you change your view position ?
Also, is your audio hardware configured properly ? GSX uses surround sound, if it's available but, of course, it must be setup properly so, for example, if you have configured for 5.1 speakers, but just 2 are connected, some sounds will be lost, depending on the relative viewpoint position.