HTPC for my home built projector

[Projector Project]

Hey guys, i just signed up here to get the other part of my home cinema running. I am currently a member of Lumenlab, an awesome site which has helped me design and almost finish an awsome 1080p projector! Now i just need audio! My lumenlab user name is Projecting Upside down and here is my PLOG (if anyones interested).

So here's the audio part, please correct me if i say anything wrong or have posted in the wrong section. Basicaly for various reasons, i have chosen to go for a HTPC setup to run my media through my projector. These are the componets i have chosen to run;

My pre-existing laptop (fairly decent inspiron 1520)
External USB bluray player
ONKYO 85w RMS per chanel 5.1 AMP (has all imputs besides HDMI)
ONKYO speaker set up (inc powered subwoofer)
VGA connection to projector (high quality cable)

Now im hopng you can see the missing component...
a decent external sound card! Seeing as though i am using a laptop instead of a PC i know i am greatly limited by the fact that the card must be external... i have had a decent look at theCreative X-Fi surround 5.1 external sound card, which for around $60 seems pretty good. But as i am planning on using SPDIF (optical), which means i can supposedly only use the soudn card as a passthrough... in this case would a cheaper card suffice??? I really do want full quality out of my ONKYO system so using analogue is really out of the equasion. Could anyone reccomend a card????

The other method i thought of (really by stumbling into it accidentaly) is that my laptop actualy posesses the power of 5.1 output through the internal sound card! (sigma tel). While i know that internal sound cards are... hmmm shite! does this also apply to a digital signal (as a passthrough)??? The way that the signal is aquired is through the S-video 7 pin output, which dell makes an adapter for which then travels through digital coaxial, which i can then pickup with my reciever... BUT is this solution going to cause loss of quality or distortion?

WHADDYA THINK!??!?!?!?!