First off, thanks for the comments guys, much appreciated.
@TheLaughingMan - Ive tried all those things now, and it hasnt helped unfortunately. Although in the BIOS I cant see much about setting up the audio apart an area that has Realtek enabled. Im certain they are set to default too.
@Tigger - Thanks, Ive just double checked and made sure its in the green socket.
@SneekyPeet - My GC is a Sapphire ATI Radeon HD 6570 Ultimate Edition. How would I go about checking this?