I don't have the vocabulary to articulate the concept fully, but I will make a suggestion that may be helpful. When we attend a live performance our visual cues often overcome our sonic attentiveness. Try closing your eyes as you lisen to live music and allow yourself to get a "sonic image" of the instruments or voices. Also note the quality of the sound, timbre and pitch, as the instruments (voices) interact with the environment. I have found that using this kind of reference allows me to judge the veracity of an audio system. I agree with the above posts that in my experience tube amplifiers and pre-amps are better able to achieve this sense of dimensionality and space.
