My way to audition a new DAC is with music (a) that I am very familiar with (b) with a mixture of recordings that I love and hate on the existing DAC. Recordings one loves should sound equally as good or better with a new DAC. Just as important is when recordings that grated on you with the old DAC no longer offend and become interesting to you ; these are signs you have fixed a broken area in the old DAC. The pop genre tends to be sprinkled with recordings which excite bad sound on lesser DAC's.
Most DAC improvement is in increased detail and reduced digital artifacts. DAC's can have tone color signatures (lean/lush/neutral) which will also affect your preference. DAC's also cannot produce what doesn't reach them correctly, anemic bass and blurry detail for accompanying instruments can be signs of jitter issues with the source solution feeding the DAC.
Most DAC improvement is in increased detail and reduced digital artifacts. DAC's can have tone color signatures (lean/lush/neutral) which will also affect your preference. DAC's also cannot produce what doesn't reach them correctly, anemic bass and blurry detail for accompanying instruments can be signs of jitter issues with the source solution feeding the DAC.