Short answer... turn off Pure Cabinet in the output settings.
Long story... I bought my Kemper two weeks ago and I simply could not understand how there was so much hype about this machine. It sounded like the very epitome of everything wrong with 'solid state' and 'modeled' sounds. Fizzy high end with large flabby low end and no punchy mids to speak of. All profiles sounded the same. However, I was enjoying it through my 1 x 12 Mesa cab with the cab 'subtracted' by switching it off on the Kemper. But I bought this for DI (direct input) in my home studio. It was very confusing to me as even the YouTube videos of people playing DI were better sounding so I persevered. I had bought online so I went to the brick and mortar store of the online shop I bought from and heard one there and it sounded great... was it their £1000 PA setup? The room? I was very confused and I was able to talk in detail with the guy the settings I had tried and he was unsure what else to troubleshoot or did not believe my ears. I was doubting my ears A LOT over the past 2 weeks. I went home and did some serious A/B testing.
Output 1 through my Mesa cab with the cab model off and close mic'd with an SM57, Output 2 from the main output, cab sim on. Both into my mixing desk on separate channels. Switching between them, the cab was just so immensely better and I could hear it plainly between A and B. "It just cannot be right" I thought, with the memory of the sound from the shop burned into my mind.
Let's check the cab 'simulation' options I thought, maybe something there is incorrectly locked or setup wrong... hmm... there seems to be some global override for the 'Pure Cabinet' setting... I went to my main output settings, where I remembered seeing this option, and turned it off.
O H MY G A W D
My Kemper sprang to life and suddenly I went from thinking 99.8% of profiles were bad to thinking 95%+ were AMAZING and INSPIRING. This is was everything I had held as a secret wish coming true. AMAZING DI sound, now it was better than the Mesa cab, and I spent the entire weekend playing guitar so much my back hurts today from rocking out all over my flat.
This thing is incredible but whoever decided to put Pure Cabinet on at a setting of 2 needs to be taken out back and shot! I did play with the amp a lot with friends when I first bought it, if the person needing shot for switching it on is me or my friends then so be it but holy smokes I do not think much of that option.
However, I can say that I now LOVE my Kemper and I gave away one of my 4 amps last night as I started the clear out. Kemper is 100% hands-down my best amp now and I was about to take it back to the shop.
Perhaps no one will read beyond my short answer but I thought I better record this story in case any Kemper staff are reading and should be aware that this option can be perceived to seriously diminish the quality of the Kemper sound. I have bad-mouthed Kemper to a few people over the last few weeks and now I intend to correct that but I was very, very close to returning the amp.