I quite like them too, I like the partially hidden nature of this. It reminds me of an old dark painting that you'd find in a big black frame in an old dark snooker hall
I know the kind of shot you are aiming for and I think you're getting close but this just feels a touch too dark all over. Rick's edit starts to bring it up more and making the horse more dominant in the frame helps as well.
I like the concept too, though I have no idea of whether or not you can get to what you want without reshooting. I think the light has to be more dramatic or more focused. Rick58's edit comes closer than your original edits, which are a bit too dark. Your last edit is too harsh and the color on the neck looks fake.
Maybe it can't really be done in post without making it look too processed. I could be wrong - someone with advanced skills could surely do things with software that I can't even fathom, but I personally would just reshoot with a better concept in my mind of what I want to achieve.
I was instantly reminded of a photo by the Slovenian photographer Joco Žnidaršič: The Lipizzan Horses ? Galerija Fotografija The light itself is warmer of course, but it hits the horse in a way that very specifically highlights the lines, the tail and the mane.