In all my frustration with SonicStage, I completely forgot about the other piece of software - MD Simple Burner. In reading the manual this morning, I discovered that this is the software which allows you to rip a CD and burn directly to MD. Why this requires a separate piece of software is best known to Sony.
In trying to solve the problem with getting CD information, I discovered that there's a newer version of SonicStage - 2.1 - than that offered by the support site. You get this one by going to http://www.connect.com/download.html. After installing it initially didn't work but I noticed it had added a bunch of RunOnce keys to self-register a number of DLLs. For modern Windows install packages, you should be using Windows Installer and should not be using self-registration - Windows Installer can't repair a self-registration. Anyway, I added myself to the Administrators group, rebooted, logged in, and tried to register for CDDB. This time, it worked. Registering MD Simple Burner worked too. The problem was probably just a DLL not registered correctly.
SonicStage still doesn't do anything particularly useful (it still works as a media player) as a limited user. MD Simple Burner works fine, but a little further investigation reveals that it's actually a service running under the LocalSystem account, with the Interactive flag set. Horrible black mark of the blackest possible black, darker than a black hole.
Digression: I don't mind having a service doing the work if it's truly impossible to do it any other way, but control should always be through an IPC mechanism, with the UI running under the user's normal logon session. We've discovered with Meteor that services marked Interactive only appear on the console, not through Terminal Services. Doing it the IPC way can, I anticipate, get you remote administration with little extra effort.