I think it has to do with the noise floor of the system and the lower distortion - especially IM distortion. I only say this because of my experience over the years with how our products have developed.
It seems to me that each time we were able to reduce IM and lower the noise floor I was able to hear more into the mix. So the really low level information (size of hall , air around instruments etc.) that is riding on the noise floor is delineated to a greater degree. I use human voice a lot to asses a system because we are all use to the way voices sound in the real world and in real rooms. I find if the system can give me a 'person in the room' effect I am on the right track when developing our products. Have you ever had times when you are listening and a sound or a voice on the recording will almost startle you? That's a great sign in my opinion that the system is resolving at a very high level of fidelity.
james
A superb write-up James! I know exactly what you mean when you say the voices startle you. It happens only during a live performance, either acoustic or with a very-well tuned PA system, OR while listening to a very high performance audio system. Without exaggeration, one of the best systems I have ever heard is the BDP-2/BDA-2/BHA-1 driving a pair of Sennheiser HD800 headphones. I will even go as far as to say in some ways the music sounds more alive than when we were in the studio recording it.
Some of my friends think the equipment looks too plain and bland but when they hear it, they will say things like "Oh, now I get it."
Cheers,
Antun