Alex,
Unfortunately, this area is quite device dependent. Different device drivers seem to implement it differently. And they keep changing. I had been trying to shoot at some moving targets for a while. That is why the Help file has been saying "if you have problems with it you may have to disable this option". At one point I just made sure that it worked with ATI devices.
The option uses IAMTVAudio interface to select audio mode. Ideally you should be able to select among Stereo, Mono, SAP, or Both. "Both" means both main language and second audio program.