There used to be a connector program for IBM text to speech but it's been discontinued since Squeeze, so speechd-up is now used.
From
https://packages.debian.org/bullseye/speechd-up
If you want to have sound on the console with a commercial speech synthetiser, such as ibmtts, you need a connector between the speech synthetiser and the speakup_soft module. As there has not been any usable connector since Squeeze, this package has this function. It is useless if you use a free speech synthetiser as Espeak, since a connector exists and is packaged: see the espeakup package. It is also useless if you use speechd-el with Emacs.
So if you want speech in console using Voxin IBM Text to Speech, you have to install speechd-up.
Best regards,
David