Where to get my Krell 400xi repaired or modified?

First thread ever. Cannot tell all you guys how much this site and everyone on here has helped me in the past year or so. I built my system with all the info on here. I was able to find all my equipment 2nd hand. It did sound great with a s300i, since it was china krell I got rid of it and found this 400. Unfortunately it distorts when I turn up the volume. Even at low levels the sound is compressed. All functions are fine and I have changed the source,cables and power cable. It all comes back to the Krell. Arye qb9, Rega R7, Transparent sp cables, Tara labs Ic's. Can anyone give me some advice? 400 owners thoughts? Thank you all who reply.