this thread is more of a placeholder for me, while i try to find out what the sound cvars mean.

s_mixahead
If you REALLY need to try and get every last ounce of performance out of your machine, set s_mixahead to 1000 divided by your WORST-CASE framerate: i.e. the default of 0.2 is enough to keep sound "right" at anything above 50fps, but sound mixing is so cheap that you really shouldn't need to screw around with it.
Likewise, if you have a rock-solid 125fps, you only "need" 0.08: but if you HAVE a solid 125 odds are you have so many cycles spare that you won't notice the extra microseconds that 0.2 takes, so again, you might as well just leave it alone.

s_mixprestep
does not seem to do anything of worth anymore