However I have yet to find any documentation on exactly what these do. What I have figured out is that you can use the aliases created here to make it easier to create your key bindings. For example you can create an alias that makes turning at a rate of .7 or so, and use that alias in your raw key bindings. I am sure this is not the only use for these options, so stay tuned. This allows you to do change specifics down to the nitty gritty, and use the aliases which you defined above.
Ambient sound is sound which sounds the same all around.
This changes the scale of ambient sounds in relation to other sound effects. Changing this value should not result in a change in performance. This is simply a matter of preference and fine-tuning. This can vary from card to card. The more channels used the better 3d effects you will achieve, however if your card does not have enough channels, it may go into software emulation mode, which would drastically slow down the game.