I think ckemper is fully aware of the fact that emulating "the speaker/"the cab" is still a challenge, and will always be.
I keep making the same experience like the Captain mentioned: When using headphones, it just doesn't sound and feel right. However, things completely change as soon as I move some air. With my Neumann nearfields, even at low volume, it is just pure fun to play. But what I like about the KPA is, that if you neither like the headphone sound, nor enjoy the signal via fullrange speakers, you can disable that cab sim altogether and use your favorite guitar cab.