In addition, he took masterclass with renowned artists such as Irwin Gage, Ernst Haefliger, Arleen Augér and Phyllis Curtin.
In addition, he has accepted numerous invitations to guest appearances at renowned German and European theatres and has performed with many major orchestras in Europe and North America.
A main focus of his vocal performances is the song repertoire, especially the lesser known works of the 20th century such as those by Ferruccio Busoni, Ignace Strasfogel or David Diamond.
Brun's regular piano accompanists include Kolja Lessing, Brian Zeger, Jan Philipp Schulze, Ulrich Eisenlohr and Christoph Hammer.
Further highlights of his career were the Europe-wide live broadcast of his song recital Flies, you of my youth dreams from the Beethoven-Haus in Bonn, the first performance of Antonín Dvořák's song cycle Zypressen in the original version for voice and piano in Ludwigshafen am Rhein and Ljubljana, a US tour with Jan Philipp Schulze and the double production of Gian Carlo Menotti's The Telephone and Carl Orff's Die Kluge in Basel.