Horrible Creative drivers and hardware? Just Google it. Seems like no matter what they do, there's ALWAYS somebody having this sort of problem with every soundcard they've made since they started making PCI cards, or at least since the Live.
His CPU time isn't being eaten up intermittently, is it? Even though the Audigy is hardware-processing, it could still cause such a problem.
P.S. -- Thank you for spelling stuttering correctly.