For reference, the 96KHz, 192KHz numbers we're talking about do not refer to anything that has to do with what the human ear is capable of. It refers to a sample rate, which has to do with the signal quality, and more specifically the resolution of the signal.
Picture for yourself a curve on a graph and imagine that that's a sound wave. That sound wave is an analog signal; it has infinite resolution because it is the pure, original sound source. A computer however can't record that infinite resolution, since we'd.... need infinite space, essentially. So what happens to that sound wave when we record sound is we dice it up as it's played and therefore save ourselves on space needed. This same process is done by a DAC when it's outputting analog sound, but in reverse. The sample rate numbers we're talking about just refer to how often a DAC records (or reproduces) a bit of that sound wave. Just like a low-resolution screen, a sound wave sampled with a low sample rate is blocky compared to one with a high sample rate.
Now to one of your more specific questions, if you have a sound card that your computer is outputting through and it is limited to 96KHz, it is probably going to limit the overall output to 96KHz because its hardware is incapable of processing anything higher. I'm pretty certain this would be true for digital and analog output.
I also think it's worth noting that if you're outputting DTS or Dolby Digital to a receiver, those formats themselves are limited to a certain sample rate, while only newer HD versions of those support the higher sample rates. As said before, this is a moot point for most games since their own sample rates won't exceed 44.1KHz, but it's worth noting if you're really concerned about it and want some perspective.
I hope that helps!