Compressed/lossy audio formats present certain limitations, and the more compressed they are the worse the audio quality will get, no matter what device is playing them back.
With MIYO, whatever quality the source material is, it will be faithfully reproduced without coloration of any kind. In fact, you might learn to hear the artifacts associated with compressed formats more clearly with MIYO – their sonic signature is readily heard if the playback chain (DAC, amp, phones/speakers) allows. Even still, a 320kbps stream ('high quality' from Spotify) might sound just fine to you, and MIYO will certainly convert and amplify that sound as well as anything out there. Trust your ears, above all else, and don't let anyone convince you otherwise.
A newer service called Tidal is actually streaming CD-quality audio, and they have a free trial. If you're curious how uncompressed formats sound in comparison, it's worth a listen. And you can check out this A/B test they developed to see if you can hear a difference with your system it's pretty neat: http://test.tidalhifi.com/