[Plugin: W3 Total Cache] problems in configurations

Here are my problems:
I use a subdomain for all my uploads, but it was not configured in W3 Total cache because I couldn’t get it to work (posted a topic – http://wordpress.org/support/topic/399182?replies=1).
I created my subdomain pointing to the default WordPress uploads directory, which is /public_html/wp-content/uploads.
So what I did was change the settings in the media upload configurations – full URL path to files – so that all my uploads were directed to the subdomain I created.
In that folder I have .htaccess with the following code:

#Expire Header
<ifmodule mod_expires.c>
<filesmatch "\.(ico|jpg|jpeg|png|gif|swf)$">
ExpiresActive on
ExpiresDefault "access plus 6 months"
</filesmatch>
</ifmodule>

To make sure these images are cached for a long time.
But YSlow keeps telling me to add Expire headers. Probably from all the files in my template which are not there. How can I Specify page headers expiration for all images? How can I do this for all the other files not in that subdomain?

Another thing YSlow keeps telling me is that I have misconfigured ETags.
How can I correct this? I search in a lot of forums and the code they tell me to insert just gives me a 500 error. I assume this is probably a conflict with the code W3 Total cache inserts in my .htaccess.
The code I tried was:

<Directory /usr/local/httpd/htdocs>
    FileETag MTime Size
</Directory>

and also:

# Remove ETags
FileETag none

Both give me 500 error.
Can you help me with any of these questions?
The ideal would be to finally be able to configure W3 Total cache to accept my subdomain settings and be able to transfer all my images, minify css and js to another subdomain using W3Total cache, instead of doing it the way I am doing now.
Thanks for the attention.

http://wordpress.org/extend/plugins/w3-total-cache/