14 (Unter dem Milchwald, 1972), based on the "play for voices" by Dylan Thomas, premiered at the Hamburg State Opera in 1973 and staged again by Staatstheater Kassel in 1977 on the occasion of the opening of the documenta 7.

He frequently uses literary sources for his compositions—for example works by Nelly Sachs, Ingeborg Bachmann, Clemens Brentano, Dylan Thomas, Federico García Lorca, Friedrich Hölderlin, Juan Ramón Jiménez, Ezra Pound, or Arthur Rimbaud.

His own individual system of notation mediates between tonality and atonality, which he says opens up a creative domain "providing for sounds, lines, colors and forms which serve to sensually enhance a desired expression."

His style has progressed from an atonal phase, when he was working on the opera Eli and "was unable to endure smiling," to a language of sounds which enable him to express and convey sensibilities, to "make them singable."

While Steffens’ occupation with this work by Sachs expanded his spectrum of compositional expression, especially with respect to dramatic components, he considered his second opera Under Milk Wood to be "an opportunity to concentrate on the configuration of comic parts within a basically lyrical style."

The book Vom Klang der Bilder, published on the occasion of the exhibition of the same name in the Staatsgalerie Stuttgart from 6 July to 22 September 1985, has an appendix with a list of paintings set to music by Steffens and other composers.

The initial silence at the beginning of the work gradually takes on elements of sound, swelling towards a sonorous crescendo, an ominous audio-pictorial intimation of the approaching fighter-bombers, before the viola intones its elegiac theme.

Because of its graphic qualities, the score pages of Guernica were included in the 1986 exhibition Linien, Briefe, Notationen (Lines, Letters, Notations) at the Städtischen Galerie Lüdenscheid.

In the afterword to the score Steffens writes, As a child I lived through bombing raids on Dortmund, the menacing drone of bomber formations and the jarring terror of low-level strafing attacks.

Numerous works by Steffens, especially those from recent years, are listed in this database, e.g., musical compositions on pictures by Peter Paul Rubens, Rembrandt van Rijn, and Emil Schumacher.