The HD-800 for orchestral and opera although also great for chamber and solo instruments, specially piano. The HD-600 if money is an issue.
Listen to a well recorded Decca or Reference Recordings of an orchestral ball-buster (ie: Richard Strauss, Stravinsky, Rachmaninov, Respighi, Ravel, etc.) and you'll need a diaper. With the HD-800, you are in the hall sitting in the best seat in the house.