It strikes me that in assessing hi-fi we're hoping to find equipment that reproduces the sounds we know are made by the source that's been recorded. But what do we know about the sounds that some sources make?
If we're talking about acoustic music, we're on fairly solid ground (allowing for a multitude of different recording locations, techniques, etc.) as we know what a guitar or violin sounds like when plucked / bowed etc.
But if we're considering any music that is produced electrically or electonically (amplified guitars, synthesisers, etc.), at best we're seeking to reproduce the sound made through the amplifiers and other gubbins used by the group when they perfom live.
For many pieces or tracks even this isn't the case, the music being created not as sound waves in the air but as (these days) 1s and 0s within the recording equipment.
Thus, with this type of music how can we really assess the veracity of our hi-fi? Aren't we at best saying that the sound that it produces pleases us (not unimportant in itself, of course), rather than being a high fidelity reproduction of the original?