cache files from static subdomain

I have a www domain and a static (sub)domain using a virtual host. I activated it via CDN Enabler plugin. That works, I can see images are served form the static domain.

I manually setup caching in htaccess. However, all files from static domain were not cached. Someone recommended using a caching plugin with cdn support.

So In intalled WP Super cache. It works for files from www domain. But not for files from static subdomain.

I tried enabeling CDN in WP Super cache (and disabled since it didnt work).

So, what goed wrong?