I can't help you with the soundcard issue, but you could probably get better help here:http://www.avsforum.com/avs-vb/forum...sprune=30&f=26
If you just need a BluRay player, this one is highly recommended:http://www.oppodigital.com/blu-ray-bdp-80/
I agree with fsrenduro, you need to move the speakers out to the edges as far as possible. This will widen the soundstage. Also, your speakers have a switch to augment the high frequencies for "behind" screen" placement. You should use that setting. A perforated acoustically transparent screen is not really "transparent". It will have 3 to 5 dB of high frequency loss through the screen. The switch will help compensate for that without ant external EQ.
Also, a perforated screen will comb filter the mids and highs. You want to keep the speakers 12 inches away from the back of the screen to help reduce this comb filtering. I would contact Stewart and ask them for their recommendation of the "best" distance, but 12 inches ought to be enough. Also, a little "toe-in" is recommended for the L/R speakers.http://www.stewartfilmscreen.com/res...esidential.pdf
Finally, the CC should have the tweeter at ear level. It looks a little higher than that in your picture. It's also higher than the L/R tweeters. Can you adjust the shelf it's on to lower it so the CC tweeter is at the same height as the L/R tweeters? This is not a huge issue, and if the shelf can't be moved, it can probably be completely corrected by simply tilting the CC down slightly to aim it at the listener's ears.
Good luck and enjoy those speakers.