This assumes you have already successfully compiled the HiFi interface in Ubuntu 16.04.
Install pavucontrol and festival:
sudo apt-get install pavucontrol festival
Run festival and the hifi interface in separate terminals.
Open pavucontrol and click on Recording tab.
In QtPulseAudio select Monitor of Built-in Audio Analog Stereo .
Feed text to festival:
festival> (SayText "Hello World!")
or for feeding a text file
festival> (tts "/home/hifi/frostpoem" nil)