My impressions of the sound quality from a Pro-ject Stream Box Ultra S2 vs a PC laptop or an iPhone running off of its battery only through three different DACs: Audioquest Dragonfly Red, Rega DAC, Denafrips Ares II:
The streamer made all three of these DACs sound better. Key improvements were a broader soundstage, more precise placement of instruments/voices, better bass definition, and a better sense of musical flow. Not sure if the difference will be the same from an iMac vs my PC laptop. Also, adding a jitter reducer such as an Audioquest Jitterbug can be worthwhile as well for more of the same benefits as a streamer provides.