I checked your site and it seems to be validated now.
X theme is good for newbie and intermediate users. The demos and the customizer manager will help you easily start your own site by utilizing the demos or use the customizer manager to have the same X theme settings from one installation to another site installation.
Pro theme on the other hand is good for intermediate and advance users, designers, developers or someone who want to create something beyond X theme especially in lay-outing the header or footer.
PRO offers the header and footer builders that give you extreme possibilities to design your header and footer.
Hope this helps!