reducing the stimulus is good,
but eventually he will have to adjust to life on life's terms,
but
if you tried everything else,
this is a hard one,
try overloading him for a good long while,
what this will do is possibly reset his tolerance levels,
this does not always work and with many children it don't,
but when it does work it works wonders,
other things to try is distractions,
find something you agree with that he can or may obsess over,
this in its self will reduce some of the issues,
but just beware, you give him something to obsess over and then
distract him in some other way it may set him off,
the down side to this is its only a distraction, the issues would remain,
he needs to learn that the world is not always going to cater to his needs,
he may be shutting down because he knows how you will react.