Terrible Booms

@stani19,
I don't think that your room is an issue. But your speaker placement might be. I have a pair is D48R in similarly sized room and don't have any boom. How close are your speakers to the walls on the side and behind? I have them on granite base. My speakers are 70" from back wall and 40" from the side walls. All distances are from wall to face of tweeter.
Now that you have got accustomed to the "scale of music" that these speakers produce, you will be super disappointed by going to a smaller speaker. Experiment with loudspeaker placement and you should find a spot that will take away the boom. Good luck.

@soundsrealaudio,I own the newer D48R and while 20Hz is too ambitious a claim, these speakers go down easily to close to 25Hz. Example is "Fading Sun" from Tejre Isungset's album "Winter Songs". I would suggest OP to rather scale down to the ProAc D30, if everything that was suggested above does not work. By disconnecting the lower 6.5, he would be killing the scale and hence the performance of this amazing loudspeaker.

@stani19,Good to know that your problems are resolved. And it is a WIN that you can keep your D40R.

I don't know how to insert photos of the system to show it ... if this is possible tell me how to do!

The best way to do this is to create a "system" on audiogon. When we click on your name we will be able to see your system. You can post the exact pic and let me know how your problem was resolved. But I am glad that it is resolved.