This post was clearer than your original, and I think we agree more here than we did before, which may partially be an issue of communication styles/methods/etc.

I believe the problem is not that of finding an objective morality given people's preferences, it's objectively determining what people's preferences should be.

This I agree with, but it's more for the gut response of "I don't trust people to determine other people's values." I wonder if the latter could be handled objectively, but I'm not sure I'd trust humans to do it.

There is an objective best ice cream flavor given a certain person's mind, but can we say some minds are objectively more correct on the matter of preferring the best ice cream flavor?

My reflex response to this question was "No" followed by "Wait, wouldn't I weight humans minds much more significantly than raccoons if I was figuring out human preferences?" Which I then thought through and latched on "Agents still matter; if I'm trying to model "best ice cream flavor to humans", I give the rough category of "human-minds" more weight than other minds. Heck, I hardly have a reason to include such minds, and instrumentally they will likely be detrimental. So in that particular generalization, we disagree, but I'm getting the feeling we agree here more than I had guessed.