What will a streamer add?

[Confused]

I have a D250 that I originally had connected to the Moon MIND but the app was cumbersome and unreliable.I have abandoned the MIND. I went with the streamer originally on the advice of my audio dealer. I then tried AIR and found it too unreliable and frustrating although the sound quality was amazing. I have since gone with a mac mini/ separate HD using a Belkin Gold USB cable to connect to the D250. I blind tested the sound using Belkin Gold versus AQ Carbon vs Nordost Blue Heaven. I had several friends over with high end audio systems and they all picked the sound with the Belkin Gold USB. I was shocked at the difference in the interconnects sound quality. I have Magico V2 speakers and I am very happy with the SQ in my set up versus AIR.  I went with the mac mini as I was looking for sound quality but also cataloging of music and the easy functionality of the iTunes interface.

So how does the sound quality of a Mac mini via USB compare to AIR Ethernet?