Per my understanding from back in the day when they first started appearing, the Sonic Maximizer is an "aural enhancer" that functions by manipulating the "pyscho-acoustic" properties of sound. It does this by applying micro-delays to certain frequencies so that your hear those frequencies as being more (or less) prevalent when in fact they are actually not.
So, it is not an EQ, but can appear to have a similar effect...
I am not claiming to be an expert by any means and it has been over 20 years since I used one... and it is entirely possible all of what I read was pure BS, but it was not "product literature" I was reading, so I have some level of confidence that it was factual