The MBLs are a different animal altogether. They are voiced in a way and use 360 degree radiating pattern that necesitates an almost untreated room. When we do acoustical designs for MBL it's entirely different than for other speakers.
It would be interesting for you to have the room measured. Find out what the frequency response and reverberation times across the frequency response (or 200 to 10k) are. Measure your other rooms that don't sound as good too. You may discover that while the RT is very high in this one room it is far more uniform than the others and thus more pleasing. I've heard and measured rooms that were treated, but the problem was they were treated in a particular bandwidth giving them a very unbalanced RT across the frequency spectrum--the result while the Sabiens for the room were "appropriate", the room sounded horrible due to this imbalance.
It would be interesting for you to have the room measured. Find out what the frequency response and reverberation times across the frequency response (or 200 to 10k) are. Measure your other rooms that don't sound as good too. You may discover that while the RT is very high in this one room it is far more uniform than the others and thus more pleasing. I've heard and measured rooms that were treated, but the problem was they were treated in a particular bandwidth giving them a very unbalanced RT across the frequency spectrum--the result while the Sabiens for the room were "appropriate", the room sounded horrible due to this imbalance.