Unfortunately my naturalist approach does not seem to disagree with your 'platonist' approach in any explicit way. I don't use such ambiguous terminology as naturalism or platonism because they don't truly describe anything meaningful in most cases about someone's theory but rather provide good arguments in of themselves for the creation of a theory of ethics. It's in identifying what these arguments we have chosen are and then elucidating their aggregate form that our position is known. Thus your statement that you are a platonist is as meaningless as saying you're a male or a female. This does not shed light on your position in the least although it gives a vague impression of what you're getting at. You call your approach antinaturalist but from my paradigm it's not at all, it's only from your side of the debate that the distinction exists and thus the debate would devolve into definitional semantics where you call something not naturalism that I at the same time call naturalism.
Although to be honest I would avoid calling anything naturalism or not naturalism in the first place because this is a distinction I do not recognize as valid. On the other hand the arguments that compose your position may be something we disagree upon. Alas with the better sense of your position you've given me it does not seem that we disagree on really anything except for semantics and I'm uninterested in a semantic debate. There's still a large portion of your position which seems ambiguous to me and may indeed be something I disagree with but I'm not going to strawman your position with assumption of what that interpretation is.