Hi,
I have just configured a site with MAXcdn.com. They provide a guide but it is not designed for xcart 4.4.x.
The guide can be found at
http://www.maxcdn.com/features/integrations/x-cart/
Would be worth xcart contacting MAXcdn to give them a more accurate guide.
I will provide my integration for xcart 4.4.x when I get a chance.
Also when I get results of how good this tool is for site performance