Thanks for your reply! I did install ADE 1.7.2, and even the previous version of Sony's own library software for maybe driver updates (of which there were none), but no luck at all: in ADE 1.7.2 my device doesn't show up either. What's more, I have a PRS-300 lying around, and that also doesn't show up in either ADE 1.7.2 or 2.0.
Tested in on two different Macs now, both with the same unfortunate results.