It is hard to characterize E.S. Posthumus. The Wiki describes their music as a form of modern, classical music.
Here is their song, “Nara” from their 2001 debut album, Unearthed.
The group was the creation of brothers Helmut and Franz Vonlichten. Sadly, Franz Vonlichten died in 2010, and his brother released their last song in November of that year, a single entitled “Christmas Eve.” Helmut is now releasing music under the name Les Friction.