Once the .sit file is open, there is a replacement icon inside. Throw out the original that was initially installed in the game folder, then replace it with the one in the .sit folder.
Be sure that you are launching the game from the icon within the game folder in your Applications folder. Moving that icon can generate multiple errors. Rather, right-click (ctrl+click on a single button mouse) the original and select 'Make Alias'. That alias can be moved to your desktop or dock for easier launching.
If the crashing persists, deselect "Disable mouse acceleration in game".