Me too I've thought to gamma issues, but in 3dsmax I've plaied with all possible combinations: I've switch On gamma, tried off, tried with different gamma values, tried to play with Vray Color Mapping but nothing...

About Post-Fx Option, this is the screenshot of Vue Standalone:
http://www.ossosso.com/public/scambio/03_vue.jpg

I've noticed that if I select the "main Camera" in 3dsmax (xStream version) and I click on "Edit Object" button, I can change the "Auto-Exposure" parameter, and other like "Gamma Correction", "Natural film response"... but effectively it haven't any effect on the final image, so I assume that the xStream version blocks in some way the "Advance Camera Options".

Is there any other way to apply Post-FX Options on the xStream version?