I think that the only possibilities here exist in how a DAC actually plays back music.
Let me explain what I mean by this, because its very common in the world of computers to over-optimize specific performance or "cheat" in certain respects.
So when you are playing music, there are many tones playing at the same time. These tones are obviously the music itself which is compromised of possibly 50 different tones at the same time, vs 1-2 tones at once. Therefore DAC vendors can indeed optimize single and dual-tone performance far beyond that of say 50 tone performance and without that multi-tone performance measured it leaves room for error.
A DAC does not produce 'music' or 'separate tones' at all. It gets instructions which voltage to create and a short time later (the next sample) the next voltage to make.
It does not care if it is 'music' or a test signal. It doesn't care about frequencies, phase, amplitude at all. It just generates the 'expected' voltage at any point in time.
Interpolation (in a clever way) calculates the most probable in-between values when oversampling or converting to less bits (DS).
It really is only re-creating a varying voltage over time dictated by the applied sample values.
Nothing more nothing less.
There is no magic. Just clever coding and electronics.