Michael, I have no doubt the X3s will sound great in your main listening room. The max dimensions of my room are 20' x 15' with an 8' ceiling, and they sound amazing to me. The room is far from a regular rectangle, for instance the short wall behind the speakers has a jog in it such that the right side of the room is 20' long while the left side is 19'. Because of this the right speaker is 6' out from the wall behind and the right 5'. Speakers are 29" from the side walls.
I know you sometimes come through my area and you are welcome to hear my X3s when things get back to normal.
Here's a diagram of my room, if they can sound so good in here, they might be ever better in your room. The speakers are in the 15' wide part, chair is in the 13' 9" wide area, and behind the chair it's 10' 11" wide.
Speakers are 7 feet 8 inches apart inside edge to inside edge. Distance from each AMT driver to the sweet spot seat is 11 feet.