so i just finished building my hack pro and it's running like a dream. the only thing i need to sort out is the optical audio. i'm using this machine is a media workhorse so all music, tv and movies will be watched using it and my home theater. i've searched endlessly and, maybe i'm just blind, but i can't find a fix for enabling the optical out on my p7p55d-e lx. i have stereo sound but want to use my 5.1 to it's full capacity. can anyone help?

specs:

p7p55d-e lx
i5 760 2.8
geforce 9500 gt
4 gig ram
snow leopard 10.6.4