Make any adjustment to the CSSMenuWriter/cssmw/menu_ie.css, as your <!--[if lte IE 6]> conditional will call on that one for IE6. The other stylesheets are working fine for the newer browsers, so best leave them alone.
Perhaps you can (in the menu_ie.css) ul#cssmw li span a { rule, use a minus top or bottom margin (one or the other, not split) value as you did in your regular stylesheet.
Maybe:
margin: 0 4px -4px 4px; // might be a starting point