Sound Stage and Imaging

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!

The best imaging is very hard to achieve. It is impossible in some rooms. The speakers have to be in symmetrical identical environments and have to have identical frequency response curves from 100 Hz to 12 kHz. This is difficult to achieve without digital signal processing. There can not be any serious phase aberrations and all drivers have to be time aligned. Full range loudspeakers with subwoofers are the best way to achieve this. The fewer analog crosses the better. Digital crossovers are better but rare. There is only one preamp that has them and that is the DEQX Pre 8. There are commercial dBx DriveRacks that could easily be used in a home system. Sanders uses one with his Model 10 loudspeaker.

Coming up with an entirely analog system that images at the state of the art is a matter of sheer luck. I use to sell and install systems in a previous life and I have heard only two such systems do it. It also requires the right live recordings. With studio recordings image "depth" is a matter of how much echo is applied. I view studio recordings as a different form of art, fun in it's own right, surrealistic.