The SAPI5 are certainly not as good as some of the other ones that are 'TextAloud' compatible. However, I think that those ones will not work in Blitz3D.
I just installed the Cepstral Character Whispery voice.
Works fine in Blitz3D - It was $6.99 USD - so it cost me about £3.50.
You can download and install demo versions: The trial period is not time-limited; It never expires. However, a voice will interject reminder messages into the audio output until you purchase a valid license key for it.
https://www.cepstral.com/downloads/
Will probably require a reboot to work with Blitz3D, but should work in Windows Speech straight away.
EDIT:
You can listen to the voices here:
https://www.cepstral.com/demos/
I just installed the Cepstral Character Whispery voice.
Works fine in Blitz3D - It was $6.99 USD - so it cost me about £3.50.
You can download and install demo versions: The trial period is not time-limited; It never expires. However, a voice will interject reminder messages into the audio output until you purchase a valid license key for it.
https://www.cepstral.com/downloads/
Will probably require a reboot to work with Blitz3D, but should work in Windows Speech straight away.
EDIT:
You can listen to the voices here:
https://www.cepstral.com/demos/