My reply to this will be short, but I figured I should post it nevertheless.

Most of the usual points were covered in the quoted portion of the OP, so I have nothing to say about them. I think the issue is consent, and not because animals can't consent, but because they can't consent to us. There is absolutely no way to know whether or not an animal is fully consenting to what we're doing. Domesticated dogs, for instance, tend to view their owners as the leaders of the pack, so to speak, and so them not eating your face for initiating sex with them is not indicating that they're okay with it. There is also no reason to think that they share the attraction, as most species (though certainly not all, as was mentioned in the quoted section) have sex strictly for reproductive purposes and not pleasure, and thus would have no reason to mate with a human.

Inertia: Your latest post somewhat answers itself. That "pizzlies" exist proves that grizzlies and polar bears can reproduce. Moose (particularly young males) seem to have a habit of attempting to mate with anything mooselike in appearance which, while unproductive, does seem to suggest that species is a determining factor in their choice of mates. Orangutans are apes and, while not as close as chimps or bonobos, are genetically (and, compared to non-apes, appearance-wise) similar to humans. You will note that they do not attempt to mate with canines, felines, marsupials, or any other kind of mammal, nevermind non-mammals. And even if this did prove that they were open to the idea of having sex with animals outside their species, it says nothing about animals that aren't bears, moose, or orangutans, and I dare you to try and get frisky with any of those.