The illusion of soundstage.

Right, comb filtering is also created when sound reflects off a side wall and travels 2 different distances, that's why lack of acoustic treatment can ruin the spacial information. 

I know little-to-nothing about much of this discussion but I know what Wolf Garcia said is absolutely true.  IIn a stereo recording it all starts with the image created by the engineer's panning of the individual tracks/channels/mics. 
As to soundstage presentation in a mono format--I don't get the concept at all.

tostados, agreed, the engineer 'sets the stage'...virtually, but that's the modern recording studio for ya....not to mention the other 'enhancments' that can be dialed in.

I suspect that given current tech might allow a certain level of 'ambiance' in a mono recording that comes through with a high quality system, but I've never had the pleasure to hear such.  On the other hand, I'm not disposed to go looking, either...*G*

I am repeating what I've heard from Roger Paul as an explanation for the quite wide, deep, and high sound stage I hear with his X-10 MkIII amp used with his X-10 line stage.

Apparently, every amplification stage passes some frequencies through faster than others. This means that even the best speakers are asked to reproduce all music with out of phase frequencies. Somehow he can sense this happening and assure that all frequencies pass at the same time.

The results are a sound stage with great realism, clear sense of room boundaries, player noises, clear decay of notes, and presence of performers. I suspect that my BMC Arcadia front and back firing speaker can reproduce all frequencies as they were recorded. 

The H-Cat components, speakers, HFC cables, Archiving Vinyl music server, and Tripoint Troy Signature all contribute to what thrills me on every album.

     I had some excellent Classe equipment given to me, two Classe preamps and two amps. One amp was 350 wpc ad the other 150 x 6 or 300 x 3. The preamps were their soul/marketing mates.
     One channel of the stereo amp was out due to blown fuses.
     Interestingly, the single channel had a huge sound stage. From a 35 year old B&W DM 14, a model known to center the sound between speakers, and the sound was all over the room. I can't imagine anything other than a design of contrived electronics that caused this.
     I never even tried the Classe pieces on my B&W 803's because my pair of Audire amps and preamps sound much better, with precise location of the instruments in space.
     Having said that, off course speakers send a larger sound than their driver width!  Speakers radiate outward in a cone. They are not lasers.