As I understand it, a "truly balanced" component would have four separate amplification circuits inside: Left plus and left minus, and right plus and right minus.
If you started out at the output of a good digital board that supplied these four separate feeds, and then stayed fully balanced from the DAC filters and outputs, through the preamp, and finally through a power amp, all with separate audio channels plus and minus for each of the four signals, and finally combined the signals at the speakers, you would actually have a useful balanced line system. All common mode distortion would sum out of phase and cancel at the speakers. This would include distortion that the electronics designer did not know existed in the first place.
Of course this will cost about twice as much as a two channel system of the same design. The musical performance gained by this significant extra cost will vary depending upon how much distortion was there to cancel in the first place. With so-so electronics, the improvements would be substantial, with really well done electronics, the improvements probably will not be cost effective.
We have tried this here in house with interesting results.
Regards,
Frank Van Alstine
