There are different types of DAC's and different types of output stages.
NOS (non-oversampling) tend to do something simple, like just using a cap as an output stage. These can sound very smooth, but tend to get congested on complex music and don't necessarily have any kick to them.
Cheaper DAC's generally use op-amps, since they are inexpensive and easy to implement. The good news here is that if they put them in a jack, you can easily replace them with a better op-amp and get a dramatic improvement in sound.
There are many expensive DAC's that use op-amps also, but their output stage tends to be far more sophisticated and the sound shows it. I would not presume to replace op-amps in those since you are paying for their tailored sound.
In general op-amps can add a punch and dynamic to the sound that may not be there otherwise. They have more PRAT (pace, rhythm and timing)
Then there are DAC's that use discrete output stages, some using tubes and some not. These can be a mixed bag, but the expensive designs get that PRAT and the texture and the smoothness and all the good things that each of the other approaches bring to the table. But you have to pay for that level of engineering and expertise.
Enjoy,
Bob