Preamp matching for Krell FPB amplifier

It seems to me that the obvious choice would a Krell preamplifier such as the KRC, KRC-HR, or the KRC-3. That being said I am sure that there are other manufacturers whose preamplifiers mate well this amplifier. The Krell amplifier is a pre Cast technology FPB. I was hoping to find out what current and previous owners have used and what kind of system integration was experienced.
Thank you for your assistance in this matter.

Drew