Hi,
First of all; You said, you are having hard time to change the "category browse page" to "flexv2", And only it woks if you change it through individual category.
You should have "nooverride" for all category, and then, once you change it through VM Configuration (which is "global") then it should changed for all categories. But sometimes it fails to be applied in all categories and this is because of the permission problem. Because your "no override" selection to any category doesn't get applied. In this kind of situation, the easiest solution is to change to "flexv2" for all categories one-by one. It is a Virtuemart related issue, because our VM Template has no influence in Virtuemart Backend.
Secondly, I am little confuse here, because the "zoom effect" is valid in product details page, which is not-related to category browse page. I don't understand how possible zoom effect finctionality can be effected by category browse page layout. They are independent and completely different pages. No matter what you choose for category browse page, this has nothing to with the zoom effect since zoom effect only functional in product details page.
Thirdly, i am seeing there is no jQuery conflict in your website but you have made lots of "customizations", you might have deleted some necessary lines to make the zoom effect get working (by accidentally). I can't help you now until you get back to original layout, otherwise i might need to spend hours to figure out what line you might have been deleted which was necessary to run the zoom effect..
Regards.