PROAC D48R Bass Booming

Go to a home store and ask for some pipe insulation. Measure the opening at the bottom of your speaker (looks like four or five inches). They make pipe insulation out of foam rubber and many different sizes so get some big enough to block the bottom of your Proac. This will cost $10 - $15 dollars.

My friend has those Proacs in a room twice the size of yours and they are outstanding. He also is using a subwoofer with a high pass filter. I really think that that room is too small for those speakers. Changing the amp will not resolve the problem!

Your getting some great advice here. I had a similar issue with myD-30R’s. Bass was overpowering my room and sounded a bit sloppy at times. Did the easy stuff first, trying to position them correctly.
This helped somewhat. I then replaced the stock spikes with a set of Audio Points which made a huge improvement. Not only was the bass tighter and more defined, but the mid range and top end improved as well. The D-48R’s are wonderful and capable speakers and worth the time and effort to get right. Good luck

Have you considered changing to something like a Lyngdorf TDIA 2170 or 3400. They are fantastic units and I can almost guarantee it will resolve your bass problems. The Room Correction software is really amazing IMO with no downsides. 

I had Proac Response 5's and D30 R's and had similar problems with too much bass and my room was much bigger than yours. The two things I did that helped were 1, run the speaker cables to the top binding posts (of the speaker) and jump the bottom. This will give you less energy to the woofers. If this method removes too much bass you can try a diagonal jump which is half way between the two methods.  2, if you use Roon, use their EQ function and cut the deep bass by however many db's it takes to reduce the excess bass. I first measured my room and found out at what frequency I had excess bass....Hope this helps.