A reader of my previous note wrote to report the same problem with Showtunes on her PowerBook. I've emailed Nonesuch to see if they have any insight.  

Metropolis did write back, saying there's no copy-protection on the Gary Numan album and they weren't aware of any problems. Their official guess is that my copy is defective, so if I send it in, they'll mail me a replacement. My Showtunes experiences makes me doubt that this will help, but the two cases may end up being unconnected.