I'd appreciate if VSL would inform us how to set things to that there's no dynamic compression or expansion applied to the instruments.
That is not going to happen, because when the samples have been normalized, you can't reverse it. Think about it. Every note on an instrument has it's own dynamic range. On a flute, for example, the higher register can go much louder than the lowest register. So you would have to set the dynamic range separately for each register of each instrument. I don't think that's even possible in VI Pro. And even if it was, it would be a crazy amount of work.
So, the Natural Volume feature in MIR can only be an approximation. It means that the loudness of the instruments are generally balanced against each other. But it won't account for the cases where you play the lowest note on the flute, and assign a cc 1 value of 127. It will be too loud compared to the rest of the instruments (simply because the low notes of the flute in VSL have the same dynamic range as the high notes, which in reality, they haven't). That's where we'll still need our brains and our ears. But in my experience it's less of an issue than you'd think. In most cases the balance is good enough that it won't disturb the 'reality' of the mock-up. And in the very few cases where it does: simply adjust the volume a little.
So, I guess, if you don't want to think about balancing and volume, you'll have to buy samples that are not normalized. But even there you'll have to mix. Even in recordings of real orchestras recording engineers will have to make subtle adjustements to balance the volume, so you can't expect samples to not have that problem.
On the bright side, from all the mock-ups I have heard, volume balance was rarely the main point that prevented it from sounding 'real'. Usually there are a whole lot of other problems in a mock-up that give it away.