High quality DACs are not just about transparency (preamps are more about that), they are about dynamic range and resolution…so with a good DAC the separation between sounds is clearer, there‘s more detailed to be heard that is more definitely placed / locatable in space.
Lower quality DACs will sound a little flatter, muddier, a bit more constricted. Plenty of people will say this is all psychoacoustics, but I can say from experience & blind testing that to my ears the differences I hear between eg a focusrite entry level audio interface and my UAD Apollo or an Apogee Symphony or Lynx Aurora are definite and drastic.
In a way there‘s no such thing as a transparent DAC, they all have their own sound signature in one way or another, but I know what you mean, a good DAC will make everything sound so much clearer that it could be also called more transparent.
EDIT: forgot to mention Apogee above as one of the companies to look at for high quality conversion, so adding it here 
EDIT2: on sampling rates…technically they shouldn‘t make a difference, but personally I FEEL a difference between 44.1 and 88.2khz or 48 and 96khz…just that little more vibration in the subconscious range I feel…though this one could well be psychoacoustics, it’s a pure feel thing and I don’t know if that would hold up for me in blind testing 
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