As for the sound I just have to say for me the sound is vital. It's like 30% sound and 70% visual (maybe even more balanced). I look like a complete noob when playing with winamp on or no sound at all.
On a map like urban2 I can pretty much pinpoint where the players are, the fewer the easier. Because of that it may look like I have a wallhack sometimes.
and it doesn't matter if you have just plain stereo or 6.1. You have to use a headset if you really want to pinpoint people.