Let me try rephrasing the questions:

1> FFXIV crashing when you alt-tab in Full Screen mode, is it a limitation of FFXIV or is it a DirectX issue? I do not have this problem playing other games in Full-screen mode, ie. World of Warcraft
2> FFXIV does not work with Crossfire in Windowed mode, is it a limitation of FFXIV or is it a AMD Catalyst driver issue?