I've been obsessed with this because I keep on going to live orchestral concerts and noticing how much darker the strings - especially violins - sound than sampled. I have been experimenting with doing various EQs. No settings that are "out of the box" are really like the live instruments. Recording engineers probably don't like this but I think the frequencies above 5000 hz should be almost gone, it is that extreme of a difference.
The question is why. It may have to do with the amplitude of those frequencies - they fall off more quickly with any distance or any absorption in the room. A recording studio and particular microphones negate this natural effect, leading to excessively bright violins.
Also even cellos can sound nasal. Another thing I have noticed between live and samples is cellos in an orchestral setting never sound "boomy" or deep, but almost always do with samples. There is a setting in MIR that somewhat accounts for this - "clean low end." But you can go even farther and add more EQ in the low range.