Krell FPB differences

My personal Krell evolution. KAV300i to KAV250a to Long auditions with the FPB 200 & 300, to finally purchasing the 200c and after a year upgrading to 300cx. Conclusions;
1. The cx version is more open and musical.
2. The first generation FPB was a little dark for me.
3. Biwiring to B&W N802's seems to draw more juice from the amp and the 300cx seems to like it better when you ask it to 'put out' (like a motor finding its optimum RPMs).
4. Upgrading my amp is now the lowest priority in finding musical nirvana.

My experience going to a 400cx from a 300 is the 400 definately beats the 300 even with the stock power cord. I really dont know why Krell made the decision to use a captive cord. But a 1/2 hour with a file, wire cutters and a 20 amp iec. I am happy as a puppy with 2 tails, using my Synergistic Research DR squared.

Does anyone have any thoughts about the difference between the 300CX, 400cx or the 350Mcx amps. Other than the power differences is there any sonic advantages to one or the other. I currently own a FPB 200 and I am in upgrade mode but my local dealer is no more and the closest is a plane ride away.