So I tested your request on my lab and I couldn't do the exact page. I was able to do the homepage and even with HTTPS enabled it will not work. Regex didn't solve it,
Using your logic of not allowing users to download from Virtualbox.org but not block the page, you can use Content awareness. Build a custom app for the URL (virtualbox.org*) and use content aware to not allow download of ANY file. Set the action to block and that would allow access to the page but not to download anything from the site.