I play through the AG-200, and completely agree with you regarding the quality of the amp. Breathtaking...It's like playing through a high-end mini PA.
I have had zero issues with mine [
he said, firmly knocking on wood 
].
Have you tried playing your K&K equipped guitars directly into the Carvin without the Red-Eye preamp, and with the amp's "High Z" button engaged? I find the sound quality doing this to be pretty much indistinguishable from going through the Red-Eye and then into the amp with the "Hi-Z" off. So, in my experience, the Carvin not only sounds better than any other amp I've tried, it does so
EVEN without the help of the preamp!
Outstanding amps. I'm glad you got your issue taken care of.