From whence does Sound Stage come?

OP:

I think you completely misread my post, let me try to clarify.

Diffusion and reflection are two different things. Just like in light, reflection produces a mirror image, but diffusion produces a soft, random re-direction of light or sound. In light, you'd achieve diffusion by looking through frosted glass.  Lots of light fixtures use this.

Yes, you can calculate reflection distances, but diffusion is much harder. Sound isn’t reflected, it’s scattered, so it produces a steady stream of arrivals instead of 1 solid spike.

Imaging is enhanced by adding diffusion at the points of a cross (looking from above). Behind the speakers, to the L and R (direclty to the sides, not at 1st reflection points), and behind the listener. These are not necessarily all-encompasing panels. Maybe 1/3 of the space to 1/2 behind the speakers, and narrowly to the sides.

@oldrooney 

How much have you actually played with speaker positioning? 

I don't know how applicable this might be for you, but I had to experiment much more than I'd ever expected before I finally got this right. One of the most dramatic improvements has been greatly improved sound-stage depth. 

There's another thread here about soundstage depth that has many tracks listeners use to measure that metric. I used some of those tracks to compare stage depth for my setup. It's quite amazing how much care some artists put into their track's productions. 

I used to confuse soundstage with ambience. Sometimes I wanted better sound stage, but I really wanted more ambience, and vice versa.

If you are using a DAC and solid state amp, soundstage comes from the recording, speakers, speaker placement and angle, and room in my experience. I find a turntable and tube amp can make a difference too. It sort of makes sense when you think about it.

Now ambience, that is something different. Lots of things affect ambience. Ambience is not only on the recording. It is something you create in your room to make yourself think you are listening to a live performance. Ambience is fake, but it sounds great.

@erik_squires You are correct, I didn’t understand what you meant by the term ‘diffusion’ and confused it with reflective surfaces in the sound path which are treated with absorption; thank you for the full description of what diffusion is, why it helps, and how it can be created. 
 

@stuartk I haven’t played with it much; downstairs the system is in a ‘temporary’ location and I don’t want to invest too much time on them, but they are on casters. If I can clear the floor space, I will experiment. I have PS Audio’s test CD for the purpose. Upstairs, the tweeter towers are screwed to the walls, I may be able to tweak the bass cabinets a bit, I’ll try it, they aren’t that heavy, but I can’t move them far as they’re tethered to the tweeter columns, but I can try different things, that’s why I bought the test equipment. 
 

@simao I’ll try to find those threads, sounds like they would be worth a listen. 
 

@othercrazycanuck I like your distinction. Using your terms, I want more ambience in my system for every recording so that when one comes along that has some staging, I get the full effect. I fear that may be a challenge for the system upstairs (with speakers against the wall), although I really like the quality of the sound I get from the McIntosh speakers. The system downstairs, with the B&W 801 speakers offers greater opportunity for tuning, the speakers seem to be much clearer and have much better imaging. Thanks for your response.