Some people want their DAC to sound like nothing, similar to how some people believe that the best preamp is just a passive one with a quality attenuator - nothing but a straight line with gain
This is largely a problem if one like listening to their music at very low levels.
In that case the output impedance of the passive passive pre amp screams towards infinity… and any low impedance power amp, and the capacitance or inductance in interconnects, then becomes a real (filter) effect to consider.
Many hifi designers believe you are essentially listening to a power supply that is merely controlled and regulated by your pre and power amps?
And this is also largely true.
The stiffer, and lower noise of the power supply is what does separate the men from the boys in the better sounding gear.
But, answer the OP’s question, it also makes a difference as to what the input impedance of the preamp is, and what the output impedance of the DAC is.
It the pre amp has a 1000 ohm input impedance versus, say a 100k ohm input impedance, then a 600 ohm output impedance will likely be dragged down more.
The Audio Precision measurement gear likely has a super high input impedance, so it does not likely suffer… or it is not likely to pull down the DAC’s output in any measurable way whatsoever.
Luckily, most manufacturers provide the input and output impedances of their gear. So that helps to a large degree.
