but in reality below 150-200 W does not go well
Usually when people say this, it means that the speakers require a very high current amplifier. If you are moving from the big FPB250m to a small chassis Class D amp, you are likely going to have to make some compromises in sound. I'm not saying it's going to sound bad, but none of these amps will have the current of the huge FPB250 with it's massive transformer, huge power supply and full Class A biasing. So, yes, you can probably find a small Class D that sounds good, but it is very likely not going to have the oomph and body of the FPB250.