I will agree that electrostatics should be good for opera, as they are clean and nonresonant, as a class, in the vocal range. Quads are one good example, if you can live with the restricted dynamic range.
If you didn't want electrostatics, I would look into BBC-heritage speakers, such as those made by Harbeth, Stirling, Graham, and perhaps some of the Spendor models. Though they look old fashioned, they tend to have low coloration, and the design criteria include reproduction of the human voice.
