you dont need a sound card. or an 850 watt PSU
SLI/CXFire is literally a way to use two or more graphics card to achieve better FPS
Sli is Nvidia's version.
Crossfire/XFire is ATi Radeon's version.
there's also a great deal on the samsung spinpoint right now making it an even better choice.
also six cores isnt needed for gaming and if you only edit videos of video games or anything like that you probably could just get a AMD Phenom II X4 955 CPU
instead of the 1090T