Cross Site LoadMovie and ISAPI Filter

I have the following scenario:

I need to distribute my swf and flv files acoording to client IP origin.

I am using ISAPI Filter to do the URL redirect.

My apllication uses HTML/Flash AS2/Javascript

My ISAPI filter redirect the SWF/FLV/XML calls other WebServer.

I putted a crossdomain.xml file on the main server but it is not working fine. The first movie is loaded correctly but fails when this movie uses loadMovie and loadXml.

Question: Both are necesssary crossdomain.xml and System.allowDomain() or just the server file addresses the problem?

Restrictions:

- I can not redirect all the content due to cross site scripting issues (javascript)

- I dont have acess to FLA files (they are third party elearning content). So I can not assure they are using System.allowDomain()

Am I missing something?

Thanks in advance

Alexandre