I knew Daniel personally. We both worked at the Orsay University for some time. We also regularly met at organ concerts in the church of Orsay.
He helped me learning both LaTeX and MusiXTeX at the same time. We also had fruitful discussions about how to improve the sound of an analog electronic organ by knowledge of electronic filters.
I have always recognized Daniel's influence on the MusiXTeX style in French-sounding commands like \hpause, \alaligne, \alapage, etc. I will always sadly remember Daniel when typing such a command.