Set StylesXmlPath with JavaScript

I have been clearing my cache and I cant find any mistakes.
For debuging i just have a plain xml file.. rather than the dynamicaly generated xml from the php file.

This is the code:

ed.Config["EditorAreaCSS"] = '/cms/css.php?site='+siteid;
//ed.Config["StylesXmlPath"] = '/cms/cssxml.php?site='+siteid;
ed.Config["StylesXmlPath"] = '/cms/styles1.xml';
ed.SetHTML('<p>test</p>');

Do you have any ideas where the mistake might be??
I promise the syntax of the XML is correct.

Thanks

alfonsoml said that it should work.. so hopefully someone else has actualy got it working?
It would be really useful if someone had a working example.

At the moment the Styles drop-down just contains the default Styles.. Marker: Yellow, Marker: Green, etc

Thanks

EDIT: Sorry I did not make it clear that I am wanting to change the XML file dynamicaly, not just once before initiating the editor.
I thought I might need to re-initialise the editor but could not find a way to do this so abandoned that line of thought.
I submit that the documentation of FCKeditor is rather significantly lacking in areas.