To answer your charge that we are demanding a "complete" ontological explanation, I acknowledge that an explanation does not have to be exhaustive to be true, but it must be causally adequate.
You have either denied or expressed agnosticism about real moral incumbency, without which there is no such thing as morality. Explaining morality away is no way to explain it. The subjective feelings that you referred to that one ought to A vs. B, if Bertrand Russel is right, are "but the outcome of accidental collocations of atoms". Since there are no good and evil atoms, not only does atheism provide no foundation for morality, it destroys rationality itself right along with it because it means that you do not hold to your beliefs because they are true, but rather because of a series of chemical reactions.
As C.S. Lewis said it (#149), "Why this stream of exhortation to drive us where we cannot help going? Why such praise for those who have submitted to the inevitable?" Moral praise and blame in an atheistic universe makes about as much sense as condemnation of the moon for its orbit around the earth.
You say that you have provided a rationally coherent and consistent atheistic account of morality. If so, then you are the first in history that I know of who has solved this problem.
Cordially,
You have neatly illustrated why communication between us is fruitless. You know The Truth, that morality must be grounded on "real moral incumbency" (whatever that is), and therefore any explanation that doesn't include that is no explanation at all.