Thanks. I couldn't find any mention of the different ATRACs in the manual, but I did find it in the minidisc.org equipment browser for the quite similar MXD-D40. You are correct. Although the D40 has ATRAC-R and the D-400 ATRAC-S, I am sure it's the same result, in that you get the better ATRAC in real-time copy only. I wonder, then, exactly what ATRAC I'm actually getting with the hi-speed copy!
This situation is unfortunate, but I will have to live with it. When I really need high-quality, high-speed copies I can use my Aiwa CD-R, which of course simply transfers bits as they are, at whatever speed. I can then at a later time, if I need to, copy at 1X to MD (I have an SCMS stripper that makes this possible).
I also find that the hi-speed copies are fine for the Clarion MD in my truck, although that doesn't do LP2. Thanks again for your response, it was most helpful!