As a more technical elaboration, rationality is a computational process involving prioritized search. It's a specific software algorithm. “Intelligence augmentation” is not well defined, but generally involves increasing the computational power of an existing human brain, aka making the hardware faster. That says nothing about the software running on it. But it is easy to show that if you increase the computational power available to a rational agent, you get a more rational agent (but increasing the computational power available to a non-rational agent would not magically impart rationality).