Clio09 - I didn't know either until I looked closely at the specs in the manual (after finding the sound somewhat unsatisfying). And, indeed, one of the interesting things about silver wire is that it sounds sweet in the highs. But to me at least, the lower mid-range and bass are weak and somewhat bodiless; hollow. Over a period of time, I get fatigued by it, and, in every instance, have switched out to copper wire and been surprised at how much more robust it is.
Just my ears, I guess (although I've found a few others that hear it similarly). Many people think it's a great pre-amp.