Some very expensive transformers work well, but I'm old enough to remember some very nasty transformer coupled amplifiers. To work well, a transformer needs to be driven by a low impedance and be carefully loaded at high frequencies to control the self-resonance. And then there is the core saturation distortion, which perhaps is a matter of taste, i.e. some people like it. That may be part of the attraction of tube amplifiers. The lesson from the Aphex Aural Exciter is that pure fidelity is not what people like to hear. I think an expensive transformer that makes life easy is perfect for many "audiophiles".