I would emphasize that what you end up with is not a "moral system" in anything like the traditional sense, since it is fundamental to traditional notions of morality that THE ONE TRUE WAY does not depend on human beings and the quirks of our evolutionary history

Are you sure about the traditional notions? I don't see how you can base that on how we have actually behaved visavis morality. We've been partially put to the test of whether we consider morality universally applicable, and the result so far is that we apply our moral judgments to other humans and leave nonhuman animals out of it. Maybe on occasion people have found certain nonhuman animals to be "immoral", but my sense is that people simply do not judge nonhuman animals on a moral scale. Conceivably, if we met a sufficiently intelligent alien species we might apply morality to them, but this is a portion of the test that we have not been put to yet.