For a pure DAC, only the SNR numbers matter. The better the SNR numbers, the more transparent/non-coloring, it will be. So when comparing 2 different DAC-AMPS (because all of these devices will have some amp section as well), the objective way is to compare the SNR values of the DAC section. Everything else will be subjective, which is also important, but not a way to compare the technical abilities of a DAC.
