Accessibility - Screen Readers and TTS

In terms of requirements for 508 or WCAG, you are not required to add an audio version of the text on the slide. It is far more important to get things such as ALT and using semantic HTML (making sure heading use appropriate heading levels, bullet lists are bullets lists etc). These support screen reader users much better. Text to speech does not contain the same level of information that screen readers do. A screen reader helps the user indentify elements on the slide such as buttons, radio buttons, check boxes etc. I can't see a scenario where a screen reader user would opt to use the text to audio content as they would have to continually switch between the two in order to identify elements to select such as navigation etc.

Some users may like to use the audio in the course as a preference, but it is definitely not a requirement. I think time/money is much better invested in all the other things and making the screen reader experience as good as possible, as this supports assistive technology in lots of ways.