Newbie Question: Why do you need a PreAmp?

Preamp serves far more than a switching device and volume control. It is literally the heart of an audio system. Ask anyone who owns, for example, a Hovland HP-100 Preamp, CJ Art II, or ARC Ref 2 mark 2. Music takes on a continuity, flow, and emotional drive that a passive just can not communicate. I have done A/Bing with several top passive units and they seem clear but lifeless with little micro/macro-dynamics and other qualities that tell you "transparency" to an inferior source or software just does not cut it and "transparency" without emotion is pointless. Ask someone with a cheap or poorly designed preamp and they will scramble to a no preamp option which is somewhat of a loss since music, it has been correctly stated, is the "shortest distance to the soul" and your heightened emotion in your listening response tells you how close you are.

In the 1960s, a famous designer of tube amps said "If it sounds good but measures bad then you are measuring the wrong thing" . Distortion is a point on a graph, a sample point like a frame from a movie, and does explain why most people prefer today's state of the art tube/tube hybrid preamps over DSP generated sound fields. Some have argued that it is how tubes distort that makes them so pleasing. I suggest that there is, not a small bit, of arrogance on part of some engineers going on here assuming you know what single point measurement contributes to better overall sound. That is why, many, if not most, serious designers of hi-end audio use listening tests to verify or refine an audio product including Sonus Faber, Audio Research, Conrad Johnson, Talon, Wilson Audio. Some things are truly explained by point measurements, the derivative in calculus speak, but can not explain the complex information under the graph, the integration, that makes for a totally immersed listening experience.