Confused about Krell FPB 300 400 200 Amplifiers

I have auditioned a Krell FPB-300 and an FPB-200. There was a large difference between these two amplifiers. I am in the market for a new Krell amp, but I can't decide between the FPB-300cx and the FPB-400cx. I understand there will be a large difference between these two amplifiers. However, I would be satisfied if the FPB-300cx performed as well as the FPB-300. So, I have two basic questions:

1) Is the FPB-300cx comperable to the FPB-300?

2) How much benefit is there to monoblocks.

Any and all input will be appreciated

Thanks,
jjmali