Can you accelerate brain waves externally using an amplifier and send it back to the brain to get faster reflex and some more power to the sensory organs?

Answer 1

The short answer is no.

reason being the speed of transmission has more to do with the medium(the thing it travels through) then the actual wave signal itself, so unless they found a way to completely reconstruct your nervous system with a different material it's pretty much impossible.

regardless, the speed at which the signals travel are already faster than you think.

most of the time spent in your reflex actions is at the brain or muscle level, so what you are asking for really isn't an amplifier for brain waves to travel faster, but rather an amplifier that allows your muscles to move faster.

Even if something like that is invented, there'd be a limit to how much speed you could gain as well.

For example, maybe it'd be possible for you to be as strong as a bear, pound for pound, you'd never be literally as strong as a bear in your current body size. in fact, if you were to possess such great strength with your current muscles, you'd rip your own arm off every time you swing it with full strength.