This name is a favorite of the Dutch royal family and has also been born by many a Dutch noble. Personally, I like the name, especially the way it ends in -ix, but I can never get past the snooty, pink-polo-wearing, upper-middle-class vibe I get from it, so I would never use it.
Derived from Philips of Marnix, Lord of Saint-Aldegonde (1540 – 1598), commonly known as "Marnix van Sint Aldegonde", so his surname was perceived as a first name. Marnix itself is a town or region of unknown meaning and location.