Oh, I'm pretty sure that I do compensate in my expression based on the environment to some degree. For instance, in this post from a technical forum from several years ago, and I don't think I really seem like an INFJ from anything you can see readily...
It would be impossible to guess my type from that post. So I do agree that there's a degree of compensation...There is no option to do this in Snes9x itself, because all of the SNES's audio goes through the same chip. Some games have internal options for adjusting the volume of the music, but many do not. This is not a problem for most, and would be difficult to implement at best, and impossible at worst. In any case, it is unlikely to be added to a future version of Snes9x.
An effect close to what you are trying to acheive can be produced in ZSNES by disabling the first five sound channels. It is not perfect, however, and portions of the background music are still played.
Even if this were possible, you could not use Winamp or any other audio application to play background music whilst the emulator was running. Two applications cannot play audio at the same time, unless of course you have two sound cards or a very advanced sound card and special drivers. You could however play the music on a stereo separate from the computer.