I'm only guessing, but if you increased the width of two sidebars by 30px each, you may want to start by decreasing the size of the main content container by 60px and increasing the main sidebar by the same amount. (Boy, does that sound oversimplified!)
It sounds like you have that last part covered.
"I've figured out how to increase the size of the sub sidebars and the main sidebar..."
#content { width:540px; float:left; padding:14px 15px 20px 22px; display:block; overflow:hidden; }
#sidebar { float:right; width:340px; padding:0px 3px 0px 0px; }
#l_sidebar, #r_sidebar { float:left; display:block; width:160px; margin:0px; padding:0px 0px 0px 10px; }
...that's strictly a wild guess. And I think maybe a bad one as well. If you try it, back up the style sheet first just in case.