Ok, so just to summarize to make sure I'm on the same page. You are trying to have a menu similar to Affinity, when you click on the hamburger menu it slides down and has content in it, images, lists, etc. Screenshot if you can view it below.
Currently, Im seeing nothing when I click the hamburger. So you are trying to use the menu/nav burger to open this?
I think I would probably use a div tag, create/add your own hamburger icon, then have it viewable on all devices. Then use a transition and positioning to create an animation type opening (almost like a modal window) but would come from the top down, then when it appears, have the inner div tags, content, layout etc. appear but only after the main "nav menu" is viewable. I know that sounds like a ton, but I can try to duplicate what you're trying to accomplish on a test site and see what I get.
I would think if you have hamburger menu in the open state you should be able to do what you're trying. After all, it is just div tags. I'd have to play with animation on the menu to accomplish the same goal.
Let me know what you think, I have some time I can see if I can make it work on one of our sites.