[NTG-context] Unifraktur Maguntia features

Hi all, is there somebody among the ConTeXt users, who has experience with the font UnifrakturMaguntja (http://unifraktur.sourceforge.net/maguntia.html#)? I tried all kind of approaches to get the font switching between lnum, tnum pnum and onum. — I come to the conclusion that I am unable to subtract and add features. I appreciate any help. Please refer to the appended tex file. Kind regards willi