I started from the very beginning and got it done. I only made one mistake, which I will correct--I mistyped the domain name. I still don't know what I did wrong the first time I tried installing, but it's of no consequence now, as things are working correctly.
I am now trying to add Speakup support but am having trouble obtaining the speakup-tools package. I've written to debian-accessibility about it and will probably have an answer forthwith.