Peter, I am no teacher, so I hardly could give lessons, but if you wait until I grow up, it could be possible!
I like your comments about Birgit Nilsson's performance, it gives me another reason to understand what happens to people who don't like opera singers (even when they like the melodies and expression involved) : they generally hear opera singers through a CD, an amplifier and the ominous speakers or headphones. Then what happens when the great Nilsson sings to her maximum power, in a voice and orchestra climax of drama, and you are not in the theatre? You turn it off. Me too. You don't feel raised up from your seat with emotion, you just feel pain in your ears.

One of the possible exceptions I know of, is the recordings made by Herbert Von Karajan, because he always spent half his time in the recording studio, and what we hear in his CDs is what Karajan wanted us to hear.

Yes, our opera house (Teatro Colón) is one of the best in the world, told by top performers. I've sung there, just in the choir, and it is an incredible experience. After my pants dried up a little, I started to enjoy the rehearsals and concerts, because I could hear MYSELF among the other voices, that phenomenal is the acoustics.
One last thing regarding classical voices: there's not only opera (which is musical theatre). There's oratorium, chamber music (where you'll never feel anything hard on your ears), French and English and Russian and American songs, German lieder, AND of course, there's Paul Robeson.
Thanks, Alice, I always enjoy your valuable contributions, and will try to hear you.
Un abrazo - Andrés