It really takes very little computing horsepower to play back audio, especially if you aren't doing any fanciness with equalizers or crossfades. But if you're using your machine for heavy number-crunching and playing audio files at the same time, you could have some problems. I've had some pretty nasty ground loop problems, running audio from the line-out. None of those problems with an external USB DAC, though the sound quality hasn't just blown me away. How you convert from digital to analog, where that conversion takes place, how whatever signal goes from the PC to the amp will make a big difference. The specs of the PC used, above a fairly low threshold, should not.
