the real amp sounds a little more... rounded? The Kemper feels a little more forward in the mix, the real amp feels a little more natural somehow, not sure exactly how.
My feelings exactly. I think people like how Kemper "cuts" because it gives you more high mids and presence, but in my recording experience it becomes a bit too shrill. When you dial it back to cut some of the harshness, the tone starts to feel a bit thin, which is why I stopped using it for recording (in my particular context). With real amps you can make EQ cuts and still feels full to me, but of course YMMV.