The latency issue would be in the timing of samples between the sound drivers, not from the game to the sound port. The sound data could take 50ms+ to make it through the DAC, but as long as it plays the signal to each driver with enough precision relative to the other (and assuming the response of the driver is sufficient), your brain would get the orientation info. The frames you're seeing are already around 50ms late for most games anyway (unless you're playing the game at hundreds of fps, which is very possible with cs1.6), and mouse latency is between 50-100ms.

Head tracking wouldn't be necessary because you're always looking straight at the screen and the camera is always aligned with your character's head. You're never going to physically turn your head to get a better angle on a sound source, you'll just turn in game.