I have a Sony MZ NH1 and a stereo mike for same, and I can tell you I never got such good field recordings before, the quality is A1.
High Density Mini Discs is the way to go as far as I'm concerned, the only thing that comes anywhere near them is the early Creative with the microphone 'Line-in' which they don't make any more, but are still available as a refurb from their own site.
Giok