Maybe it's the firewall in XP. Works on my laptop with Win2K.
Anyhoo, here are some thoughts:
- Is there any way you can relocate your seating position away from the back wall. Nasty acoustics at room boundaries.
- If possible plan to have your mains forward of the monitor/entertainment unit.
- {unrelated} You might want to consider making future pictures smaller on your site.

It's tough to suggest much with a basic picture. The best advice I can give is to sit down with some graph paper and draw the room to scale. Make scale cutouts of all the furniture and speakers to be located in the room and then start shuffling them around.
Good luck.