PROAC D48R Bass Booming

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

Looking at reviews on your amp it was noticed the bass was good but not particularly tight. Combine that with speakers that arent really known for tight bass and that may be part of the reason. Another cheap thing to try would be a Schiit Loki EQ or something similar to shelve down the low bass a bit. I find it completely transparent. 130 bucks worth a try imo. 

*What we are not seeing is his room with a multiple of 2 and having full Range Speakers positioned in the corners is the challenge*.*Because of this (any full-range speaker) in the corner will be up 9 to 12 DB * because of the corners of the small room are near the speaker. Its not the speaker fault or amps (((extravaganza recommend amps which reproduce tight bass))) No leaner wire or amp will fix this magnitude of an issue. If amp manufacturer made an amp that its frequency response was down 9 to 12 DB at 80HZ that amp would be considered broken.
If bringing the speakers closer doesn’t solve. Vandersteen makes an analog nondigital assessment box start at 20k then 33k move up to 50 K and higher until the problem goes away finalize with the specific X2 High Pass 140 bucks
Schiit Loki EQ = 150 Bucks would also take down excessive 80 Hz bass.
Put Felt on the wood surface under the ports. once installed your in-room bass response will be more neutral try going back to where the speaker’s position sounds their best.
Best, JohnnyRAudio Connection