The Beast being a Strix (or at least related to them) is hinted at several times. I like this idea of lowering shadow blood potency by shedding baby Strix.

I always took vampires to sort of be two-souled (kind of like Durkon in OotS); the Man is what is left of their original human soul and the Beast is the Strix-soul. In Kindred, the two are partially fused and fight for control, with Humanity sort of representing how much influence each has.