A PSU calculator said a Sound blaster with a front bay would take up about 12 watts. I'm not sure how this would compare to the xtreme gamer, but I suspect the different with or without it would be minuscule. I'd worry more about it handling the 7900gs; with or without the sound card...
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Desktop * Athlon X2 4200 | 2G RAM | 160G HD | 7600GT
Laptop1 * C2D T5550 | 3G RAM | 120G HD | Intel x3100
Laptop2 * C2D T5250 | 2G RAM | 160G HD | Intel x3100
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