The New York Times has an article entitled "Mahler and the Lessor Known
Stars in His Universe" that is pertinent to this thread. It discussers
Joachim Raff, Robert Fuchs, Hans Rott, and Franz Schmidt, along with
Zemlinsky, Volkmann, Bruch, and Richard Strauss. Remember, you have
to register with the New York Times to read the article, but it's free.
Definitely worth the price.
http://www.nytimes.com/2002/08/09/arts/music/09MAHL.html
Larry