In 1950 Koch became Repetitor for ballet, opera and operetta and 2nd "Kapellmeister" in Meiningen, where he was from then on promoted by the theatre director Fritz Diez. The main focus of his activity was that of an operetta conductor. From 1955 to 1958 he was 1st Kapellmeister at the Opernhaus Halle. There, in 1958, he produced the ballet "Kreuzbauer Ulrike" by Carl-Heinz Dieckmann, choreographed by Henn Haas and set during the German Campaign of 1813 to the first performance. In 1958, he went to the Stralsund Theatre as musical director. From Halle, he brought his assistant director Harry Kupfer, who was now the only music theatre director to stage the following operas for him in Stralsund: "Der Freischütz" by Carl Maria von Weber, "Enoch Arden" by Ottmar Gerster and "The Merry Wives of Windsor" by Otto Nicolai. In 1960/61, he moved as music director to the in Stendal. In 1961, he realised with the Hungarian refugee Béla Hollai in the West German Göttingen, a joint project between the Göttinger Symphonie Orchester and Stendal with works by Josef Suk, Aram Khachaturian, Carl Maria von Weber and Robert Schumann.