RE: "bandlimiting" - what is it, exactly?
Ah, that's a good article, thanks!
OK, so basically, aliasing, when reading out at a given sampling rate, will chop up the waveform if it doesn't correspond 100% to a multiple of the nyquist frequency. The closer you get to the nyquist frequency, the bigger the chopping as a proportion of the waveform (it's easier to see on a diagram), until finally the waveform bears no resemblance to the original. In fact, the fundamental frequency completely gets lost in the harmonic noise.
So: as you go up, you cut the tops. And by the time you are at 20KHz (assuming 44.1) you have just a sine wave, regardless of what the original may have looked like.
Probably the AKAI reads out the samples at different speeds rather than at a constant 44.1KHz (or whatever has been chosen). Using this technique, you go from digital to analog before filtering (I'm guessing), so the problem doesn't arise. The filters on the Z8 are on a separate option card, which may support my theory.
Thank you for the link.