It's possible that the analog outs on the i30 happen to be on the noisy side. Certainly a keyboard can be built to have virtually silent line outs. High quality components should not produce noticeable noise. Inherently, there's no difference in quality between an analog out and a digital out. The only practical difference is that the analog signal is SUSCEPTIBLE to interference/noise. Of course in practice the analog outs in a keyboard aren't necessarily going to be of the highest quality (though Yamaha's seem to be quite good in this respect), but then again the A/D converters may not be either....okay I suppose I shouldn't repeat myself....