No harm done, I almost didn't believe the 10% THD when I first read about it (despite my experience with the amp, that seemed extraordinarily high).
However, I'm not sure I agree about sound quality not being altered. My idea of sound quality is "does this sound precisely how the artist/creator/whatever intended it?" I consider any sort of noise, distortion, or even background noise to be a problem. So if the amp is responsible for the sound being noticably different from what it should be, then it definately has an effect on SQ. But that is based on my definition of amps and SQ. Yours may be different, as SQ is a rather subjective thing.