eSpeak NG Text-to-Speech is a formant-synthesis text-to-speech engine. It does give a robotic voice, but is relatively fast and simple to get going. It may thus be an interesting alternative, at least in initial trials.
espeak-ng using macports libs, configure as follows:
./configure LDFLAGS=" -L/opt/local/lib"
The rest as documented.
I have not yet tested
make install, which may require additional