This option is available as optional feature within Vienna MIR, called "Natural Volume".
Technically, the reason for the seemingly "wrong" volumes is very simple: In digital audio, there is an absolute maximum a signal can achieve volume-wise, called 0 dB FS (for "Full Scale"). If you go over this value, a A/D-converter will distort heavily during recording.
Now you might argue that we should adjust our preamps and converters to the loudest possible signal and leave these setting alone. The problem is: As soon as you leave the area of optimal gain settings, the recording will degrade in the analogue domain as well as the digital domain. So we head for the optimal resolution of (more or less) each sample.
You might say that these differences should be reflected by the mapping and programming within a Vienna Instrument. Although this would be possible, it would lead to the situation that the violin would have to be set to -20 dB (or even less) to achieve the necessary headroom for (say) a TamTam. Quite understandably, most users would complain why the violin is sooooo quiet (... and as a matter of fact this is the only complaint we get on a regular basis regarding Vienna MIR ;-) ... how good that "Natural Volume" can be switched off).
The good thing is that you are able to write a concerto for flautando violins and can rest assured that the recored samples are pristine. 8-)
HTH,
/Dietz - Vienna Symphonic Library