The best way to describe this problem is to "show it" to you in action.
Go to the following page in the official template demo:
demo.flexiblewebdesign.com/stylemart/index.php?option=com_virtuemart&view=productdetails&virtuemart_product_id=49&virtuemart_category_id=21&Itemid=514
Now, hover your mouse over the "Handbags" main menu item and when the submenu opens, try to select any of the last 3 choices ("Leather Bags", "Backpacks", "Sale"). You will see that there is no way you can select them because the "Zoom plugin" is activated.
I tried adjusting the "z-index" attributes of pretty much everything, but I failed.
This problem renders the Megamenu useless in all product flypages. In our case we do not use "Breadcrumbs" so the distance between the menu and the zoom plugin is even smaller.
Can you please tell us how to fix this problem?