This is a live site and I've settled without FancyBox because I couldn't get it to work seamlessly.
I would state the issue plainly like this: If you configure any multipage gravity form, there is no way to pop it in a FancyBox and have it remain in the FancyBox when you click the "Next" button - you are returned to the form on the page, not in a modal. An iFrame *may* solve this problem but that introduces its own set of styling issues and is a whole other rabbit hole - I was never able to get it to work right. You should be able to reproduce this problem easily by making a 2-page test form and using the standard fancybox-hidden, fancybox-inline classes for the form. First page pops in the modal, form looks great, you lose the modal when you go to the next page - you are correctly progressed to the next form page, but on the parent wordpress page that launched the form, not in the modal, which closes upon clicking next and causes a page refresh. Should be pretty easy to test. As I'm dealing with a fairly long form, even though modal popups are sexy and awesome, it doesn't do too good to have one that goes 3 page lengths below the fold.
Trying to get a business off the ground and I have too many irons in the fire. I apologize for making a support request and not having the wherewithal to see its testing through to issue resolution. Hopefully this is a clear enough description of the problem. Clicking next on a multipage Gravity form refreshes the page, which closes the FancyBox modal.
Cheers, and thank you for replying to me.