Sonics of Streaming

Reviewers, both here and in the audio press, speak of vast sonic differences among the many DAC-less streamers/network players on the market. Leaving aside features such as ease of use, variety of outputs etc., what internal design elements dictate inferiority/superiority in fidelity and the enormous range in pricing? My ancient analog brain can't grasp how Model X on a given ethernet cable can render streaming audio so differently from Model A+ on the same cable when both use the very same cables, DAC, amplification chain, and loudspeakers.

Advance thanks for a brief tutorial to guide my planned "upgrade."