How to evaluate preamps?

Based on experience, I found that any preamp, regardless of quality, degrades sound reproduction compared to a direct connection. My power amp has a passive source selector and passive precision stepped atteuator, allowing me to enjoy life without a preamp. Until now. I had to move my sources away from the power amp, behind my listening sofa, and the number of sources has increased. The need for switching between sources, and to drive a long interconnect (9m) from the back to the front of the listeing room forces me to re-visit preamps. Too bad for me.

So how does one evaluate a preamp? I just purchased two units to audition. Since I already know it is impossible to "improve" and only alter the signal from the source, I want to begin by assessing the extent to which a preamp damages the sound compared to no preamp at all. How much transparency is lost by inserting the unit in the system? If all is not lost at this point, I want to assess "how" the unit alters the signal. I don't understand the usual reviewer approach that analyzes individual facets of sound, i.e. deep bass, mid-bass, mid-range, hf, micro dynamics, macro dynamics, etc. Rather I hear different genres of music reproduction that I call "synthetic sound", "euphonic sound" and "natural sound". These are complicated to explain, but the names communicate an idea of the meaning.

Synthetic sound is typical contemporary high-end sound. My reaction to synthetic sound is "this is (or is not, as the case may be) the most amazing sounding stereo system". Synthetic sound excels at resolving detail like the number of cymbal shimmers, background sounds, fingers working frets and keys, breathing, recording session editing, etc. I can hear individual parts, but synthetic systems tend to fail at synthesizing and integrating the parts in to the whole. Or they simply distract from the holistic experience of reproduced music. Euphonic sound is just that - very pleasing to the ears. Music sounds beautifully enhanced on euphonic systems. They may or may not also be resolving and accurate - I've heard both. When I listen to euphonic systems, the experience is look viewing through a golden-tinted lens. It can be pleasurable, but over the long term not my cup of tea. Natural sound is typically unspectacular and unimpressive at first listen because nothing jumps out. No earth-shaking bass, ultra-sonic "air", or microscopic resolution. I guess they error in being subtractive rather than additive. Over time, they become extraordinary for not imparting electronic artifacts or artificial additives. To me, this is the correct approach.

An observation on the "absolute sound", comparison to live music. This is a very silly concept. First, no audio system compares to a live event. Yes, I listen to a lot of live music. Yes, I play instruments (piano now, alto sax and clarinet in the past). Yes, I have listened to some very expensive SOA systems. None of these remotely compares to a live experience. None. But what is intereting are systems that elicit reactions similar to the reactions we experience while attending exceptional live music events. In other words, an exceptional system is one that is able to re-create reactions in the listener that the listener might experience during a live musical event - not trying to re-create the sound of a live musical event, because that is an exercise in futility.

So what does this have to do with evaluating preamps (finally! get to the point!)... To my way of thinking, synthetic sounding preamps are doomed from the beginning. The perceived resolution they render is distracting and has no contribution to recreating the emotive experience of live music. Ask yourself this: when was the last time you were at the symphony or a Stones concert and thought, "I can hear the sound of Mick Jagger's heavy boots when he is strutting across the stage" or "listen to the breathing of the third chair viola in the second row". Who cares? On the other hand, on a euphonic system I listened to some of the most heart-achingly beautiful classical music (Michelangeli on the second movement of Ravel's concerto in G), and on the same system listened to Dereck and the Dominos play "Why does love got to be so sad" recorded live. Clapton's guitar was more beautiful than ever! It was a little weird hearing rock sound so beautiful, but not entirely objectionable.

So, how do you evaluate a preamp? I'm seeking one that allows me to switch sources and control volume, while minimizing corruption to the input signal, and imparting a natural sound.

Scott