He studied also improvisation with Jean Pierre Legay in Paris. A prize-winner at the J. S. Bach International Organ Competition in Lucerne, he has made numerous concert appearances and radio recordings as an organist, harpsichordist and chamber musician. For two years he was a rehearsal piano player at the theatres in Basle. and Stuttgart.

From 1994 to 1999 he was a member of ensemble Musica Antiqua Köln and performed at the world leading concert halls both as a soloist and continuo player. Since the end of 1999 he has concentrated himself on the solo repertoire, giving harpsichord, piano and organ recitals at festivals in the entire world. Rieger has also held teaching positions at the Salzburg Mozarteum, the Musikhochschule Hanns Eisler in Berlin and since 2004 has taught at the Folkwang Hochschule in Essen.