In 1937, thanks to the same Monsignor Andreoni, he obtained the position of organist Chapel Master of the Basilica of S. Maria Nuova in Abbiategrasso.
Here he could freely experiment with his new liturgical music, including the first mass, “Missa Mariae Nascenti” inspired by that church, gaining his first successes and acclaim from critics and the press.
The sacred music became the genre in which his musical genius was fully expressed.
In Abbiategrasso Daniele Maffeis is remembered especially as the author of six brilliant Operette Musicali born from (an identity of pedagogical intent) with the director of the Oratory and scholar, Don Ambrogio Palestra.
From the deep friendship established between the two educators, the musician and the librettist-poet, the world of the didactic operetta for Oratories, from elementary forms into which it had fallen, was raised to high artistic and educational levels, for the youth.
At the end of the war, he composed the “Missa Regina Pacis” which was enthusiastically welcomed by audiences and music critics.
In 1951 Monsignor Palestra was appointed parish priest and moved away.
Maffeis continued his organ service in Abbiategrasso until, in 1957, his friend the parish priest obtained the nomination in the Basilica of San Satiro in Milan and relocated him there too.