GSX never tries to handle your audio card directly, it uses OpenAL so, if there are issues with it, it can only be related to how compatible your audio drivers are with OpenAL.
Clear example of this, are such reported "volume fluctuations". GSX never change the volume, unless you explicitly move the GSX volume slider in the settings. There are no other places in the code where GSX ever changes the volume.
However, the driver itself might, to do positional audio. Even in this case, GSX doesn't do anything directly, it only specifies a position in the 3d world for an audio source, but the rest is entirely handled by OpenAL, which in turns call the audio drivers (not 100% technically accurate: it calls the audio drivers if the card support EAX hardware acceleration, otherwise it calls OpenAL, which will in turn call DirectSound, and finally the drivers).
So, whatever issues related to sound you have with GSX sounds, while the sim is running, are entirely outside our control. Well, unless you hear something clearly wrong from a logical point of view, like playing the voice of the deicer when you call pushback...