Your PSU is rated for an 80 amp 12 volt rail.
Tri-SLI GTX 470's need about 42 amps (around 500 watts). Figure 12 amps for the CPU.
That's about 650 watts. RAM - less that 10 watts per GB from the 3.3 volt rail - 60 watts at most. Two drives - 40 watts at most. Motherboard - say 60 watts. Sound card - don't know, but it can't be more that 20 watts. Fans - figure 4 watts apiece, insignificant.
That's less than 800 watts. You will have plenty of power available.