ok, let me try to understand:
/**Change**/
.myMenu ul ul
means any ul under any ul under any .myMenu class
any ul under any ul of class myMenu
/**and Change**/
.myMenu ul li:hover ul, .myMenu ul a:hover ul
/**to**/
ul.myMenu li:hover ul, ul.myMenu a:hover ul
is basically the same idea-- more specificity.
But not just more specific, but your version removes one layer from the hierarchy. Ie, the original version looks for a grandchild ul under myMenu, yours looks for a child ul under myMenu. Meaning, the original is deeper than the html-- there is no grandchild ul under the top ul.
so why would it work on the other site? Oh, i see! On the old site, myMenu is a div surrounding the ul’s, but in the modx site, myMenu is the top ul.
YOU’RE AWESOME!