I currently own and love my Krell FPB 300-C. I upgraded from the FPB 200. Obviously the C and CX versions are the newer/newest versions of the FPB Series. That being said, I never had a hick-up, concern or any issues with the FPB 200 (before upgrading). My FPB 300-C has performed equally as reliably. I have owned other Krell equipment as well (preamps) and only once had a problem with one much older preamp a while back.
I do make a point to contact Krell, sometimes even speaking with Dan D. directly. They are always happy to answer any questions and even make suggestions. My local Krell dealer is terrific (shout out to Larry at Paragon in Ann Harbor). Other than with one Preamp, my calls to Krell have always been unrelated to problems (as referenced above, never had problems with an amp of theirs).
For the sound? I love the FPB Series. I have also listened to the KAV Series and there is no comparison, FPB is MUCH better. Only thing I would say is that if you are buying an amp that is more than 15 years old, I would inquiry about what parts have already been replaced. It should be at least 15 years before any parts normally need to be replaced in a Krell amp.