although there are no difference in the actual acoustic models 1.9 vs 2.0
i do believe that the underlying HD engine was changed enough to make the models appear improved.
kind of like playing a cd through a cheap player, vs a high end player... (yes i can tell the difference)
You are correct that there should be no difference between the 1.9 and 2.0 acoustic models.
Remember I am only stating my opinion based on my experience, and that I had problems with the upgrade process, therefore, there is no guarantee that what I originally heard was the correct models for either 1.9 or 2.0. I am even unsure that my original 1.71 level was correct, because there were differences between the SEMI models on my 1.71 and the 1.9 I installed, and the SEMI models had not been updated between those releases. This leads me to believe hat I have had slight faults with all of my JTV flash installs that have somehow affected how some models sound. Either that or I have another fault in either my VDI cable or my HD500 that is causing models to sound different after each upgrade and between each time I go and experiment to listen to the sounds.
All I can report is that between 2 different upgrades to v2.0 that some models have sounded different each time, and that the rollback to v1.9 in between the two upgrades also had some models that sounded different to v2.0 but also to v1.71 which was not supposed to happen.