[triffids]

Thank you! I could not follow those instructions in ADE, and figured that there must be something really wrong with my ADE installation/configuration.

I had to not only uninstall ADE (again), but remove the digital editions .plist files in my user Library/Preferences folder. (I mention this in case any other Mac users run into this problem.) When I reinstalled after that, I got the setup wizard, it detected the Kobo and allowed me to authorize it. I was able to then add the library ebooks over (they're PDF files, show up under "Documents").

It's a relief to know that I can view library books on the Kobo after all! :-)