I have acoustic guitars and a mandolin. While sitting behind these instruments it is a little off in the nuance department BUT sitting in with others playing, there are a lot of subtle sounds that takes a pretty good recording and playback to catch (especially on mandolin). As I have progressed my system, these nuances are showing up in spades.
I have been to many symphonies and found any with a fair amount of brass and in 440 to be (to my ears) bright. Since these concerts are not amplified I would have to say that they are natural. So when listening through my system I expect that same brightness in certain instruments. By the way, for that reason I love 420 or 415 pitch or the sound of French horns. When I hear instruments through a system and its all warm, I feel that it is not true to the recording and thus is missing that natural sound and inner detail.
Don