Turns out it's only available from Audible.com, which I didn't have an account on. Bah. Oh well, sign up for free, spend some more time downloading and installing the proprietary software. Shove in my Samsung YP-U2 to download the files.
No. It turns out that Audible.com doesn't support my MP3 player.
Well, too bad. I'm not buying a new MP3 player just to listen to METAtropolis. Instead I'm deleting the proprietary software, cancelling my audible.com account, and continuing to enjoy my DRM-free listening experience. And I have been made a little more of an activist in the process.