When you use the Rift with a 5.1 Sound System,is the sound moving with your head movement? Thanks.
Depends on the setting. HMD (headphones) moves the sound with your head movement, HMD (speakers) doesn't.
You don't want the sound to rotate when using speakers, that's only necessary when using headphones (when using speakers what's behind you will always be behind you regardless of your heads orientation).
Actually it's quite irritating if games don't have a speakers option stopping the sound from rotating with your head movement as the rotation completely messes up directional audio for obvious reasons.
If you have the option to turn up the volume, always use speakers - there's nothing like hitting boost and a 135 db subwoofer shaking your stomach. No matter which headphones you use, the experience will always be pitiful compared to that.