He attended master classes with the likes of Aldo Baldin, Theo Adam and Elio Battaglia, and was taught by Dietrich Fischer-Dieskau and Elisabeth Schwarzkopf.
[1] During his studies he was engaged at the Meiningen State Theatre, where he sang such roles as Wolfram von Eschenbach in Richard Wagner's opera Tannhäuser.
From 1997 to 2005 he was an ensemble member at the Staatsoper Dresden, and sang roles such as Count Almaviva in Le nozze di Figaro, Papageno in Die Zauberflöte, Guglielmo in Cosi fan tutte and Olivier in Capriccio.
[2] Kupfer had guest engagements among others at the Staatsoper Unter den Linden (as Olivier) and the Bavarian State Opera (as Guglielmo).
Kupfer has worked with conductors such as Giuseppe Sinopoli, Hartmut Haenchen, René Jacobs, Philippe Herreweghe, Marc Soustrot, Jeffrey Tate, Peter Schreier, Helmuth Rilling and Trevor Pinnock, and has sung in concerts in San Francisco, Los Angeles and in New York's prestigious Carnegie Hall.