Ok I had time and I saw the Xmas upgrade so I decided to make a complete fresh install.
Your method works Nautica but i'm not sure the patch is really needed since it's added in the new 3.5 install file.
I even added Xmas pack after Halloween and it was working great.
But after that, I had severals problems, my antivirus and firewall were blocking and I had to add an exclusion to XSP in order to let antivirus and firewall execute it...
From now everything is working except Dungeon EX
and filemaker seems to be broken aswell, "driver0001.ddx" file is missing
But it's true that DirectX 11 improves the game it is more fluid ^^