I've heard the same about EVH's hearing, and his stubborness. You can't fault him for trying new things, especially with the late 80's boom of preamps like the CAE, Bogner, Soldano, etc. The Bogner Fish preamp had a "Brown" channel, which EVH may have used at some point IIRC. I know he had a CAE in the very early 90s, pre-5150 head. A good way to view EVH's tonal changes is to take a look at his current amp of choice... it bares little resemblance to a Marshall plexi in design and tone, that's for damn sure. But it was still a quality amp, used by many, especially in metal/thrash/hardcore. Then the 5150 mk2 came out, which was not nearly as good of an amp. Go figure.