Are you using an MM or MC cartridge and do you know the output? My thoughts are that the combination of the cart with the phono setting is somehow just at the edge of distortion due to improper loading and this is picked up by the highly resolving Krell. The Krell's inputs are hard to overload so it's likely to be at the cart/phono pre interface.
I use an EAR834P with my 400xi with excellent results (Lyra Argo i cartridge)
I use an EAR834P with my 400xi with excellent results (Lyra Argo i cartridge)