Hmmm.... Maybe I'm missing something here, but the drive circuitry inside the capsules for headphone is, by design, electrically unbalanced.
My interest was piqued so I looked in to this further. It seems that some headphone manufacturers are using the word 'balanced' to describe the method of separating the the left and right channel grounds to avoid common mode noise and cross talk, but that's not the same as using phase inversion to deal with electrostatically induced noise in long connection cables.
