DUNLAVY SC-VI

Unlike the usual equilateral arrangement, a typical Dunlavy arrangement would be to start with the speakers about 11 feet apart and the distance from listening position to each speaker of 10 feet (68 degree angle between the speakers). You might be able to get the speakers 12-14 feet apart in that room. The soundstage should be fabulous.

What do you mean by a room build?

A good friend had Duntech Princess (more similar to DAL SC-IV) in a 20x20 room with a 9' vaulted ceiling and they sounded fantastic.

HOWEVER, read any source on acoustic design and they all recommend against a square room (avoid standing wave reinforcement). I think my friend's room worked so well only because one end has a 6' wide opening into a smaller room plus an open door way leading to another room; in other words his room was not square acoustically.

I would suggest contacting Rives Audio or other acoustical designers to discuss your situation. And I will suggest that all Dunlavy designed speakers work best with placement well out from both the front and sidewalls. I would be more concerned with sidewall distance than distance between speakers (meaning 4-4.5' each side with 10-12' between speakers [centerline to centerline] in a 20' room). In my experience the 10-11 feet to the listening chair that Daverz suggested will be the minimal distance. Such tall speakers need distance for the drivers to converge, particularly time/phase coherent designs like the DAL.

Room build means that I am purpose building a room for audio listening. Everything will be acoustically optimized including room treatments. Audio processors make me cringe even though they can be very effective. I think I have the width thing down pat, I am more concerned about low ceilings. 9 foot at the front wall and 6 foot at the back. 7.5 foot ceiling height 10 feet from the front wall. This means if they are 2 feet from the front wall, listening position should have a 7 foot ceiling height roughly. Perhaps I should place the speakers at the short wall facing the other way ?

I think you want the speakers firing away from the short ceiling side so that reflections are not "focused" on the listener by the ceiling, but I don't have any empirical acoustical data to back that up.