HELP with site speeds

I have dug through a TON of articles on this topic. I am running WPMU on pSEK and am experiencing very slow loading times. I tried the recommended caching plugins all of which broke my site minus Quick Cache. I did not see much of a speed hop just with that install so I continued to research. The site of my primary concern is However, even my admin panel is EXTRAORDINARILY slow to do anything, so any help I can get is greatly appreciated! By the way, I am relatively new to all of this and am definitely not a programmer. So of the posts I was reading were a bit over my head. I can kick my way around in WP just fine, but just as a for instance I had to google how to find the htaccess file to make those changes because I couldn't find it anywhere!

I have the following plug-ins running specifically on this site:

I have the following plugins installed site wide that I was hoping to help with speed issues:
- Quick Cache
- Forced Gzip (fyi, don't think I saw improvement with install of this...only aftermaking the manual mod to the htaccess file did I see a slight improvement. I tried the zlib change to the template header file that was suggested on some forums out there, but even after manually editing the single ticks in the code it reduced my site to a screen of jumbled shapes, lettters, etc so removed that code from the header file and all was back to normal there. zlib is enabled on our server (did the test.php to find out), but I may not be utilizing it?)
-WP minify (here's an odd one...I installed this plug in; said it installed successfully, but it does not show up in my installed plug-in list. had this happen on a few plug ins lately. But, if Iook in my plugins folder via ftp I see the WP minify folder) I would also swear that after installing this it actually slowed my load time down?? My YSlow score got better, but loading seems slower! ARGH!

I have made modifications based on posts I read to my htaccess now looks like this (I never removed anything, just added snippets suggested.):

RewriteEngine On
RewriteBase /

#uploaded files
RewriteRule ^(.*/)?files/$ index.php [L]
RewriteCond %{REQUEST_URI} !.*wp-content/plugins.*
RewriteRule ^(.*/)?files/(.*) wp-includes/ms-files.php?file=$2 [L]
RewriteRule ^(.*/)?avatar/(.*) wp-content/avatar.php?file=$2 [L]
RewriteRule ^(.*/)?sitemap.xml wp-content/sitemap.php [L]

# add a trailing slash to /wp-admin
RewriteCond %{REQUEST_URI} ^.*/wp-admin$
RewriteRule ^(.+)$ $1/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule . - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-.*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

#AddHandler application/x-httpd-php5 .php

<IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off

# BEGIN Compress text files
<ifModule mod_deflate.c>
AddOutputFilterByType DEFLATE text/html text/plain text/xml application/xml application/xhtml+xml text/css text/javascript application/javascript application/x-javascript
# END Compress text files

# BEGIN Expire headers
<ifModule mod_expires.c>
ExpiresActive On
ExpiresDefault "access plus 5 seconds"
ExpiresByType image/x-icon "access plus 2592000 seconds"
ExpiresByType image/jpeg "access plus 2592000 seconds"
ExpiresByType image/png "access plus 2592000 seconds"
ExpiresByType image/gif "access plus 2592000 seconds"
ExpiresByType application/x-shockwave-flash "access plus 2592000 seconds"
ExpiresByType text/css "access plus 604800 seconds"
ExpiresByType text/javascript "access plus 216000 seconds"
ExpiresByType application/javascript "access plus 216000 seconds"
ExpiresByType application/x-javascript "access plus 216000 seconds"
ExpiresByType text/html "access plus 600 seconds"
ExpiresByType application/xhtml+xml "access plus 600 seconds"
# END Expire headers

# BEGIN Cache-Control Headers
<ifModule mod_headers.c>
<filesMatch "\.(ico|jpe?g|png|gif|swf)$">
Header set Cache-Control "public"
<filesMatch "\.(css)$">
Header set Cache-Control "public"
<filesMatch "\.(js)$">
Header set Cache-Control "private"
<filesMatch "\.(x?html?|php)$">
Header set Cache-Control "private, must-revalidate"
# END Cache-Control Headers

# BEGIN Turn ETags Off
FileETag None
# END Turn ETags Off

Conducting a YSlow test gives me the following (a score of 76 - up from the 42 where I started)...I have learned a little bit more on what all of this stuff means, but still have not a clue how to begin to correct it. Here's everything that pops back below a B:

Grade F on Make fewer HTTP requests
This page has 26 external Javascript scripts. Try combining them into one.
This page has 21 external stylesheets. Try combining them into one.
This page has 24 external background images. Try combining them with CSS sprites.

Grade F on Add Expires headers
There are 11 static components without a far-future expiration date.
(no expires)
(no expires)
(no expires)
(no expires)
(no expires)
(no expires)
(no expires)

There are 23 JavaScript scripts found in the head of the document

Grade C on Reduce DNS lookups
The components are split over more than 4 domains 64 components, 999.6K (634.3K GZip) 1 component, 0.0K 8 components, 1368.4K (1339.7K GZip) 2 components, 111.5K (23.7K GZip) 2 components, 4.4K 2 components, 62.9K 1 component, 91.3K 1 component, 1.3K 1 component, 0.02K

Grade C on Minify JavaScript and CSS
There are 3 components that can be minified
inline <style> tag #3
inline <script> tag #5
inline <script> tag #8

Grade F on Use cookie-free domains
There are 78 components that are not cookie-free

That's all I can think of to post to give you the big picture....Any thoughts or advice??