Im not saying this is the way it went down but it could very well be that Johann Pachelbell is the one that wrote the first composition using the hexachord. I dont realy know much about the hexachord except what has been written in previous post. What I do know is that Johann Pachelbell wrote a composition call -Hexachordrum Apollinis- and he is also the guy that inspired J.S. Bach. Just for further discussion It would be interesting to truly find out if Mozart had actually written any pieces with the method spoken about. Especially concidering he was in the Classical period and Bach was in the Baroque period.