Hi Federico,
I am most grateful for your comments and caveats. I rather liked your version of 'Winter' on YT. My main comment would be that the strings in the lower registers don't have quite the 'attack' of the real thing - this seems to be something that's especially difficult to capture.That the test is hard will I hope make it a good test of VSL (and the renderer).
I have been corresponding with a VSL expert and he's going to have a go at a few bars of my composition. It requires a lot of double stopping from the violins and viola and a legato line from the cello. If it turns out OK and he agrees I'll post the final result.
I have some experience with other libraries and have indeed found strings to be unsatisfactory. I was motivated by Jay Bacal's rendition of the Ravel string quartet but I'm only beginning to appreciate just how much skill was involved in making it.
Thanks again for your input - please keep up the good work!