Are you using the "space" effect, when connected at home ?
One thing (IMHO) that gives a really bad sound, is if you have the space effect left on when playing using powered speakers.
I use the SPDIF output which is routed to my Focusrite DAW. I then have my headphones connected to the DAW.
So I have to have the space effect turned on globally (not as a slot), while other use the headphone jack on the front.
When I go from this configuration and connect to my two DXR-8 cabs (and forget to turn of the space effect) the sound is really awful.
The space effect is really nice to use when using headphones but it gives a kind of nasal character if left on when using in a powered setup.
Within the "output" section there is a sub-menu where the space effect can be toggled either on globally, or on for the headphone front jack only.
I would be really pleased if the Kemper team corrected this menu to have the SPDIF output to be on when the menu was set to have the space set on for the headphones as well.
This way the space effect would always be off on the mains output.