My experience with a Rotel RA1570 integrated amplifier has been that I had to go to DAC's in the price range of the Denefrips Ares II or Schiit BiFrost to get better sound than the internal DAC. I tried several $400 DACs and none of them sounded better than the Rotel's DAC using either USB or COAX interfaces. It could be different with other integrated amplifiers.
It is important to note that better DAC's can have superior USB interfaces, filters, linear power supplies, and other features that integrated amplifiers don't have. Those features can make a difference.
I hope that this helps.