The PC you linked has a S/PDIF connector for digital audio output. Does your TV have S/PDIF input?
Speaker setup is as easy as it sounds. Select the speakers as your default audio output.
Your graphics card doesnt match the quality of your other parts. You can get a HD 4670 1GB video card for about $80.
Here is a HD 4670 1GB with HDMI for $CAD 83 SAPPHIRE HDMI Radeon HD 4670 1GB
Do you need a Core i7 860 CPU for Dawn of war 2, Left 4 dead 2?
With a $300 CPU and a $80 video card I think you can see the imbalance.
A Core i5 750 $210 CPU and a $170 SAPPHIRE Radeon HD 5770 1GB HDMI
is a much better balance for gaming.