I will suggest something else, having lived with subwoofers for several decades.
I will suggest that ATC SCM40’s don’t need subwoofers in that size of a room and will work better alone. Soundstage and coherence will be much better. I use SCM40’s in a 20 by 22 foot room and never felt the need for subwoofers.
If you do go the subwoofer route, I would suggest getting two, as stereo imaging and coherence will be better, it’s easier to integrate them in. But then that is a lot of complexity and expense.

