Amplifiers can certainly color sound, but a data conversion is supposed to be straight 1:1, whatever the spectrogram looks like is what the analog signal should be. It'd be like if your DVD player changed what a movie looked like.
So, you believe that all DVD players use absolutely identical MPEG decoding and signal processing algorithms to create their output signal? Nope. Even the
encoders for DVD movies do not use identical algorithms to each other. They all try to adhere to the boundaries of the relevant specifications, but their means of getting there varies widely, and the quality of the images they output varies widely, accordingly.
If two camera lenses are of identical size, and both are made from glass of identical degree of transparency, then does that mean that they will/must produce images of identical clarity? Nope.
They, too, will each be designed and manufactured according to certain theoretical, practical and economic constraints.
Rule of thumb: if there's an audio difference between DACs it means at least one of them is ****ing up.
There is
no such thing, in the Hi-Fi world, as a perfect Digital to Analogue Converter, up to, and including, this point in time. That fact is mathematically provable. ALL Hi-Fi DACs (and indeed, all studio Analogue to Digital Converters) in the world, up to, and including, this point in time, are flawed, to varying degrees, as they attempt to approximate the reconstruction of the original analogue music signal, from a flawed digital encoding, as best their designers (and manufacturers) can, within the constraints of their knowledge, budget, and the technical state of the art of the silicon components they employ. Rob Watts (designer of Chord Electronics DACs) is getting closer and closer to ideal DAC performance, but hasn't quite reached perfection yet. Many other DACs are mathematically provable to be substantially inferior in the accuracy with which they attempt to reconstruct the analogue waveform.
In the Hi-Fi world, Digital to Analogue Conversion is not as simple as a pocket calculator performing a '2+2=4' type of calculation. If you believe it is that simple, then you are being rather naive.