The solution to the Speech voices issue can be understood with some explanation. There are three different types of voices that can be in the Voices folder and three corresponding synthesizers -- each synthesizer works with a different voice type. The three synthesizers, MacinTalk 2, MacinTalk 3, and MacinTalk Pro, all work through the Speech Manager.
For a voice to be supported or active, the corresponding synthesizer needs to be installed in the Extensions folder for that voice type. The voices available at the Web site, Agnes, Bruce and Victoria, are MacinTalk Pro voices and require the MacinTalk Pro synthesizer to be present. The icons of the speech synthesizers and matching voices have a small character (2, 3, or P) in the lower right corner of the icon to designate their type. This supplies a visual aid in identifying the matching voice and synthesizer types. If the voice file has a generic document icon, then the corresponding synthesizer is not present on the disk.
You can run the Mac OS 7.6 installer and custom install just the MacinTalk Pro synthesizer from the English Text-to-Speech 1.5 install package. The base Mac OS 7.6 installation does not add MacinTalk Pro voices, but the Text-to-Speech installer will when appropriate. You can do this by either running the top level "Install Mac OS" application, and choosing customize for just the English Text-to-Speech package, or by opening the English Text-to-Speech folder of the Software Installers folder and running just that one installer.
For additional information search for Tech Info Library article, "Mac OS 7.6: About English Text-to-Speech Read Me."
This article was published in the 26 February 1997 "Information Alley."