Easy answer, buy a Dac with fixed output and no choice of filter. If you buy a Dac that does other thing after the output and using it as a preamp, it is a different ball game. Those expensive Dac that are so much criticized on this site have a sound signature intended by the designer, manufacturer. There is no need for AB controlled comparisons, because you are not comparing equal functions. I have a cheap topping Dac that I use with a separate preamp, I also have a RME Dac which sounds different , as explained above They are both recommended by Amir and are both great Dacs. Although I have never heard top end Dacs like the Denafrips and the Holo Audio, it is not logical to think they are useless and an intentional consumer rip off.I think you could understand that sighted listening results are as trustworthy as the fortune tellers…
Tried so many times to trick the others believing they are claiming to hear differences in sound among dacs but even using the exact recordings, once I tricked them to think the dac switched while in reality it didn’t switch, replay the same material can make them hear the difference is more than telling me what is the truth