Thanks – glad you like the theme. Unfortunately, your requirement cannot be met at present since we don’t have filter function when we try to display gallery/portfolio entries of a particular category. You can display gallery posts of a particular category using [show_post_snippets] shortcode but then you lose the filter function.
Can you pls check if the Essential Grid plugin from ThemePunch –
http://codecanyon.net/item/essential-grid-wordpress-plugin/7563340
helps achieve this. I recommend it highly when you need play around with gallery or other custom post types like portfolio.