The Zeus-R is what I'd describe as neutral/flat from a graph's perspective, wherein there are no peaks or troughs in the frequency response, apart from a slight forwardness in the mids/upper mids, and an overall dry tonality. I'd akin in it to the HD800S, which is dry and crisp, but reasonably forgiving and has a slight overcoat of warmth.
The Zeus-XIV, on the other hand, leans towards what a set of studio monitors would sound like in a room, with a bolder, larger, and warmer mid-and-mid-bass section. I find it perfect for mixing and mastering to my tastes; I always end up adding too much (mid)bass when mastering on transducers like the HD800S or the Zeus-R, but maybe those are just my tendencies/habits as an engineer.