I believe the distinction between turning down the treble and using the resistors was discussed in the following thread ("M60 Ear Fatigue" in the Stereo section--sorry, don't know how to post the link correctly):

http://www.axiomaudio.com/boards/showflat.php?Cat=&Board=ST&Number=8146&page=10&view=collapsed&sb=5&o=0&fpart=

Can't promise, but I think I remember that.