Original sentence: After World War II his position in Cologne was consolidated as he became Generalmusikdirektor in charge of both the opera and the Gürzenich Orchestra, which he conducted until 1974.After a string of recordings of Mozart, Haydn and Beethoven with the Gürzenich for a French subscription collection in the mid 1950s, he  made no studio recordings for about three decades with the exception of an appearance with the Vienna Philharmonic Orchestra on Decca Records, accompanying Wilhelm Backhaus in Robert Schumann's piano concerto (his only recording with that orchestra).In the 1970s he recorded the complete symphonies of Franz Schubert and Anton Bruckner with the WDR Symphony Orchestra Cologne
Edited sentence: After an (obviously low-profile) string of recordings of Mozart, Haydn and Beethoven with the Gürzenich for a French subscription collection in the mid 1950s, he remained outside the studio for about three decades.After the war, his position in Cologne was consolidated as he became Generalmusikdirektor in charge of both the opera and the Gürzenich Orchestra, which he conducted until 1974.An extremely odd exception was his only appearance with the Vienna Philharmonic Orchestra on Decca Records, accompanying Wilhelm Backhaus in Robert Schumann's piano concerto.His career was as little flamboyant on record as on the podium.In the 1970s, with the WDR Symphony, finally, he recorded the complete symphonies of Franz Schubert and Anton Bruckner