Room treatment I believe can only dampen or sharpen the sound rather than make it filling imo. I'm against the idea of adding a Sub woofer, want to keep it pure stereo. Hence was looking for speakers with larger drivers and enclosures.
Towers of the same family have bigger cabinet volume and more bass drivers.
But the mid range and tweeter is mostly the same size in a family of speakers.
The larger or multiple bass drivers give the room filling sound.
@mpw has recently integrated a purpose built subwoofer
I have integrated a REL T9/i into my rig.
Both the above rigs have standmounts are L/R speakers.
Adding a sub or two to make it 2.1 or 2.2 is still stereo. Check brands like REL, Rythmik, etc
They accept speaker level or high level inputs and act as sub bass units.
Don't rule out the option, since you still like the Dynaudio units.
Make friends with local FMs in your town. Check if you could borrow a suitable unit for trial.
If not convinced, start a serious speaker replacement hunt.
Cheers,
Raghu