I have a couple of BBE Sonic maximizers I use in an instrument(guitar) amplifier application and it does add somewhat significant improvements to the sound. It is one of those things that kind of grows on you. I have on occasion, disconnected one and placed it in my A/V system to see what it would sound like and what, if any changes , it would make for the better.
In this application, because of the variables in surround sound choices PLUS the much wider frequency ranges, as opposed to a musical instrument amplifier, it is far less noticeable, especially since it is designed to correct phase relationships in less than adequate speakers. In quality speakers like Axiom's all it does is allow you to basically adjust a type of treble and bass response which is really not needed and you won't really hear much in the way of changes anyway unless you are just listening to two speakers in stereo.
Having said all that, however, one thing I am still contemplating is getting one for my center channel because after playing around with this several times, I found the maximizer will bring out the dialog somewhat better than usual without any volume change and without a disruption of the timbre between the left, center and right.