Competent Modern DACs. What are they? Some examples, please, at least manufacturers or price ranges to have an idea where to look for the Wonder Land of Identically Sounding DACs.
Well, here are the specifications for Wolfson's product line...
http://www.wolfsonmicro.com/products/dacs/
You'll notice that they don't list frequency response, because all of their DACs have a sampling rate of 192kHz which according to Nyquist allows for perfectly flat response quite a ways beyond the range of human hearing. (44.1kHz covers human hearing range neatly)
You'll also notice that the Signal to Noise Ratio is at worst about 80dB and the Total Harmonic Distortion is at worst -80dB. This is enough dynamic range to push the noise floor well below the range of human hearing at even excessively loud listening levels.
Specs like this are for all intents and purposes perfect sound for human ears, even on their cheapest DAC. The better DACs in their line have more features (multichannel, onboard headphone amps, etc.)
These sorts of specs are common in all digital audio devices. Some rate a bit higher, but the degree of improvement is statistical only. It's all beyond the range of human hearing.
For comparison, let's see how the response of Dynobot's best speakers compares...
The Dynaudio Audience 82 is rated from 26Hz to 21kHz +/- 3 dB
Now for speakers, those are very good specs. But the low end doesn't reach to the lower limit of human hearing, and the range of frequency imbalance at any given point in the audio spectrum is 6 dB. Humans can generally clearly hear 1dB differences, and you probably listen to your music at a volume level of 20-30 dB. +/- 3 dB is a pretty hefty amount of imbalance. Granted, the biggest imbalances are probably at the ends of the spectrum where the sound isn't all that important to the music, but these measurements were probably made in absolutely ideal conditions. The acoustics of Dynobot's living room probably precludes these speakers of operating anywhere near the published specs. And if you put the same speakers in my living room, they would sound totally different than they did in Dynobot's.
The amount of deviation from perfect sound in Dynobot's remarkably good sounding speakers is in a whole different universe than the inaudible deviation in even the cheapest DAC that Wolfson makes.