Technically, my friend and I are both theists. It's simply a disputatio we have, so I'm the one building up the argument against myself.
I'm aware of the distinction : epistemic brute fact aren't really a problem, since they touch the intelligibility of the universe as seen by us. It's the ontological brute facts which are.
I know it's a common running objection I happen to have, but it seems I haven't grasped it clearly, otherwise, it wouldn't be coming back to my mind.
To give you an answer, I'd say : "Well, I have no reason to provide a support for this claim : first, I see no reason to suppose that the intelligibility of the universe is the default position. And second, if I were to give you a reason, that would make some intelligibility in here, thus breaking the fact by itself. The most I can say is that such a position is enough to weaken the case against theism, and this is enough for the point of the disputatio."
How to grapple with that?