Hi,
I use to have fpb 200c (twice) and fpb 250c. A few days ago I got the fpb 400cx. The 200c was cold and dark, the bass was thick and full. The 200 lacked the extrim treble, I had the fill that it look at me with "shark eyes".
The 250c was warmer with a very small tilt from the midrange to the mid-treble. The bass was thiner and quicker compare to the 200.
Martin Colloms from the magazine HFN compare the fpb 300c with the 400cx. He rated The 300 at around 35 points, the 300c at around 42 and the 400cx has lifted the score up to 65. Compare to others amp's (CJ Premier 140 rated 36 points), it's a tremendous achievement.
Tomer