Enna was primarily a composer of operas and operettas. There may be a few more orchestral pieces but I have been unable to identify them.
AUGUST ENNA: A CATALOGUE OF THE ORCHESTRAL MUSIC
1880: Concert Overture
1884: Suite for orchestra
1886: Symphony No.1 in C minor (lost)
1897: Violin Concerto in D major + (Danacord cd)
1898: Romance for Violin and Orchestra
Cantata for the Industrial Exhibition in Nakskov
1900: Ballet "The Shepherdess and the Chimney Sweep" for narrator and orchestra + (cpo cd)
1905: Symphonic Pictures "Marchen": 32 minutes + (cpo cd)
Symphony No.2 in E major: 34 minutes + (cpo cd)
Festival Overture "Hans Christian Andersen": 11 minutes + (cpo cd)
Ballet "St. Cecilia's Gold Shoes"
1907: "The Story of a Mother" for soloists, chorus and orchestra
1927: Ballet "The Kiss"
1930: Symphonic Fantasy for Organ and Orchestra
and
Ten other Overtures