My first guitar had too much treble, too. The first place I would look to is the bridge, if all else fails with set up, etc. I made mine out of ebony, and solved the problem by replacing it with a rosewood bridge. Until then, I didn't think there could be too much high end.
It could also be the physical shape of the bridge, but features usually end up dampening sound, not reinforcing it. Do you have a picture you can post?
Another approach would be to dampen the E with braces inside/under the top. My model of sound production says that the first string generates a ring of vibration, centered on the cross point of the X brace (assuming this is a steel string guitar) with a radius usually outside of the bridge wings. Try plucking the E and feeling for any hot spots of intense vibration on this imaginary ring. If you find one (or two--they may be symmetrical) try sticking a gob of modeling clay there to see if it helps. If it does, you could consider it just another "wart"
, or you could add a peaked short brace or two under that spot for an unobtrusive fix.
Scott
