Realtek, digital sound, 5.1 - no sound?

I've seen alot of these realtek threads, searched around but didnt find anything that helped me, so please help me out guys!

Just got a new computer, first time on vista, very exciting times lol!

Everythings working fine, except my audio.

Now I have Logitech z-680 5.1 digital surround sound (old school but still awesome), their connected to my computer via the optical cable. My motherboard (gigabyte extreme X-58) has onboard HD sound. The amp that comes with my sound says its detected and displays 'Optical - digital' meaning that its detecting the digital output/input etc.

However there is no sound. I checked my drivers (which are the latest) and everything is working fine.

Is there something I'm doing wrong? I had a look in the Realtek HD audio manager and everything seems fine? There's a page for the digital output, but nothing on the digital input (just says status unlock).

Help meeeeeeeeeeee.