I have heard teh Mcx 450 mono blocks and they break away from the typical Krell sound that has been described over the years. The mids are more musical and the highs are slightly more extended and natural sounding.
I went from a FPB300 to a FPB 400 cx. and the difference is not suttle. In my system the music is more involving and the improvments are across the board. Bass, mids, and the highs are all improved and makes me want to listen just that much more. Not that the 300 is bad but I could not imagine going back.
The 300 replaced a 100s I am a big fan of Krell amps imo they just sound right. I have had Levinson and Pass amps for a short time but I keep going back to the Krells.
By all means go with the latest cx amps even if you have to wait a little longer.
I basically agree with the above posts.
The 450mcx is based on the "300", which in my opinion is superior to the units based on the "200" design. But, the only problem with the newer Krells is that they don't allow for different power cords without modification.
I discussed my going from the FPB300 to the FPB400cx with an honest dealer that I have a friendship with. His feeling were that since I achieved a big improvement with the aftermarket (Pure None) powercord, I should NOT upgrade my amp.
I would love to go to mono amps (450) if I could afford it. Also, my sytem requires 2 stereo or 4 mono amps.
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.