Sound Stage and Imaging

Also of importance to mention: low bass is covered (Velodyne DD15 small room, Dayton 18" sealed driven by ED LT1300 in large room). So NOT concerned in this area.

With soundstage and imaging in mind, what helps with regard to the room:

a) hard vs soft BEHIND the speakers

b) hard vs soft OPPOSITE the speakers

c) hard vs soft SIDE of speakers

d) close or far wall   behind

e) close or far wall - sides

f) close or far wall - back 

Where 'hard" is reflective, non absorbent. 

Where for now to start NOT dipole, etc. speakers. 

Generic or General statement (each speaker is different, but some general rules apply). 

ADS "or pair of ADS L2020s, (which will fill your huge room) and / or ADS L1530s or L1230s. ": can't even find a PHOTO online of ADS L2020. The mid size LDS (L880 etc) look nice (I do like dome midrange, have a pair of Infinity Quantum 2 in parts in the basement, never heard them (no time to go over them, redo xovers). 

Can someone linke to ADS L2020?

Also as far as imiging is concerned: aren't the single speaker Kef 150 also known to produce excellent image (maybe not a wide soundstage, and may not 'sound' as nice as otheres (or may concerns, not enough AREA to 'fill' the big room, but maybe enough for the small 20x20?). 

@kraftwerkturbo 

You want Magnepan 3.7i or better. I do not like Martin Logan ESLs. The curved panel is a problem for any number of reasons. Sound Labs makes a much better ESL and you can get them in 8 or 9 foot tall versions which will fit to most ceilings forming line sources down to 1 Hz!

Speaker placement depends on the room. You need to put sound absorption at every first reflection point.

An excellent modern LS3 5A is the Harbeth P3. I recently set up a system with them crossing to subwoofers at 100 Hz. As we say in America, they kick ass!