"If there's a supernatural being somehow responsible for it all we cannot have direct epistemic access to it simply because it is supernatural. You cannot prove or disprove it exists, because you cannot do anything at all with it, empirically."
You've basically circled around to say that we cannot prove the supernatural because the supernatural is beyond proving. Why then is my example (and I'll grand it's absurd) invalidated? I could list any possible combination of supernatural forces, which would expect any manner of behavior of humans, to any result in a hypothetical afterlife, and there would be no way to disprove my assertion. If the supernatural could indeed be anything, then there are infinite possibilities. If there are infinite possibilities, then we don't even have a starting point on how it all works, how we should act, who we should worship, etc.
If you must have a more grounded example, take any of the old, dead religions, that once had large and educated followings, but no one gives serious consideration today. How does a religion become outdated? How can you be certain that their gods and their teachings are invalid and won't apply to you?
Personally I'm not married to the notion of being an atheist. I think it would offer considerable peace of mind to have some sense of how things are and how things will be. I'd love to know. I just haven't seen anything that convinces me that religion x, y, or z is a fundamental truth to the exclusion of other hypothetical truths.