When this connection is made between your disability and what you need, few professors will turn you down. It must be clear that you are not asking for standards to be lowered. You are using tools to help you perform. To pass, you must perform the task that your classmates perform. You may, however, need to get there in a different way.
Dyslexic students have to read the textbook just as nondyslexic students do.
They may just do it differently through the use of books on tape. Don't be aggressive. It isn't in your best interest to turn a professor against you. But don't be passive either. Stand up for your rights.