NO, auditory therapy did not work for my 5yr old son at all. It was a waste of money & time.
Instead, maybe you could explain explicitly to your son that he may hum only at home or in the car? Personally, I don't mind my son's humming (it's a good indicator of his mood, his anxiety level, and whether he's looking for trouble or not).
Listening programs are generally better suited for Non-AS kids. There is no empirical data supporting there use for Asperger's. As for my son and husband, both find it "annoying", not helpful.
Would it be helpful for your son to have music or a white noise machine on? Often the humming is used as a tool to block out something they don't like.
(Currently my son is humming a piece of music by John Barry from "Alice In Wonderland" ;)