PROAC D48R Bass Booming

I would recommend amps which reproduce tight bass(krell,gryphon,dan d'agostino) ,avoid tube amps

Do you have bass traps or other room treatment? I use an active bass trap instead of passive, but the idea is the same https://bagend.com/products/series/active-bass-trap/

You could also try some electronic room EQ, which should be able to fix your problem.

What type of floor are the speakers placed on? If suspending wood floor, make sure they are decoupled from the floor. You can also experiment with blocking the side vents near the floor to see if that helps.  

The first step is always proper speaker placement.  It is also one of the hardest and most time consuming pursuit.  It is not enough to apply the rough generalization that--away from the corner, bass is reduced.  You have to move the speaker inch by inch to find the right spot.  Google the Sumiko method of speaker placement. 

Room treatments might help, but, that is a step that should come after speaker and listener location changes have been tried.  With excessive bass, look to employing bass traps in the corners of the room.  Traps tend to be big, but, that size is required to tame the long wavelengths of bass sound-waves.

ProAc D48s do tend to have a full, and not particularly tight, bass response.  You can alter that a bit by, as someone above mentioned, adding some resistance to the port output.  Aside from this "modification," any other equipment change will have only modest effect on the sound.  You can try leaner sounding speaker cables and interconnects.  I don't know about the particular amps you are considering, so my general comment is that it is really hard to predict how any given amp and speaker, in any given situation, will play together; you have to try out the combination or count on luck.

Try this guide for speaker placement.

http://www.cardas.com/room_setup_calculators.php