The first obvious thing to do is to check with another pair of headphones. Doesn't matter if they are studio or not as long as they work. You can also check your headphones on something as easy as your cell phone, if you have the adapter. Also check your headphone volume level in the Kemper Output page 2.
Then contact support if all else fails.
I checked it with another a higher Impedance headphone and it was fine so its definitely an impedance thing. But as i said I'm just curious to know if kemper changed the headphone output from their earlier models as with the same settings on the head and stage they're very different.