He made a debut in Vienna in 1973 as soloist with the Vienna Philharmonic conducted by Claudio Abbado and occasionally does play solo performances. However, he has found the highest demand for his skills as an accompanist. Among the internationally famous vocal artists who have requested him for their recitals are Arleen Auger, Francisco Araiza, Peter Schreier, René Kollo, Lucia Popp, François Le Roux, Jessye Norman, Gundula Janowitz, Dietrich Fischer-Dieskau, Cheryl Studer, Cornelia Kallisch, Tom Krause, and Julie Kaufmann. Gage also has a strong interest in continuing the great tradition of lieder recitals, and, therefore, pays close attention to emerging younger singers. It is considered a sign of promise when Gage consents to appear with them in full recitals. Among these younger singers have been Roman Trekel, Matthias Goerne, Dietrich Hanschel, Christine Schäfer, Christiane Oelze, Monika Bacelli, Michael Schade, Dagmar Peckova, and Kurt Streit. He is a co-founder and regular participant in the "Freunde des Liedes" series, which, five times a year, presents several young singers. In addition to the German-language lieder repertory (from Beethoven to Hindemith and beyond), he has presented extensive concert series devoted to French and English songs by such composers as Chausson, Poulenc, Vaughan Williams, and recordings of songs by Purcell, Ravel, Dvorák, Debussy, Milhaud, and Sibelius.
He has won several major recording prizes, including the Grand Prix du Disque, the Deutschen Schallplattenpreis, the Edison Prize, and the Gramophone Prize. In 1979 he began teaching classes in lieder interpretation at the University of Zürich. He also conducts master classes in Europe, Japan, and the U.S.
In the recording studio, he has made noted recordings with Elly Ameling, Lucia Popp, Chistine Schäfer, Elisabeth Speiser, Cheryl Studer, Jessye Norman, Christa Ludwig, Tom Krause, René Kollo, Julie Kaufmann, Brigitte Fassbaender, and Gundula Janowitz. On the Arcanta label he has produced two albums of Songs without Voice (Lieder ohne Stimme), featuring Brahms and Schubert songs played as piano solos.