From whence does Sound Stage come?

In my room my soundstage was recording dependant...

The best to test soundstage is to use classical music recordings... Organ recorded in church and chorus music was the best for my test... Sometimes well recorded piano or quatuor...

I dont have experience between many speakers...

My past speakers were two-way box Mission Cyrus, and i was able to make them disapear completely only after extensive room tuning... Because each room is different i cannot help you much...But the recording is what gives the soundfield not the gear if the gear is well matched and if the speakers are well chosen and IF THE ROOM IS adapted and tuned for the speakers ......

i have no idea how to create a soundstage filling all my room apart from acoustic treatment and control... Some gear can produce a soundstage filling a room WITHOUT acoustic disposition in the room ?... I dont believe that but i want to know if it is possible ? It is not my experience but i dont have many high cost gear experience ... I manage to do it with low cost components but acoustic was the primary tools..

I remember listening Magnepan in a living room, the sound filled the room contradicting what i just said  with no acoustic tuning,  it is true,  but the sound quality was not perfect because there was no room tuning... Then i prefered my inferior designed 2-way box speakers way more adapted acoustically to my room ... Even if big magnepan can be way better in other acoustic settings.. I think acoustic is the main problem for us all...

One sadly ignored item is diffusion.  Directly to the sides and between speakers is usually an ideal place, followed by behind the listener.

Note these are not actually first reflection points. Done correctly a system will not only image but image beyond the speakers.

I think you are right on the spot...

In my room anything goes  amok untill i determined the right spot for diffusion  and absorption  and reflection time... Any small room is a puzzle ...

Personally, I would work on my system being musically engaging with your favored tonality, dynamics and inner detail. That would be my core system. Next, I would search for, or post a thread requesting great imaging recordings with a request for the contributor to let me know what aspect of imaging impressed them with the piece. Then I would work on room acoustics, speaker and listener position and so on to maximize not only the above, but soundstaging. Lastly, you could revisit components to see if different this or that might improve things. Room acoustics has to be a big part of this, but you can’t be changing everything all the time.

I had my system setup to where I thought that everything sounded great and then one day I slumped down in my chair and laid my head back a bit and the soundstage just expanded in every direction. If I were smarter, I would tilt my speakers up a bit. Today, I discovered that my amp/speaker connection wasn’t correct. I moved my speaker cables from the 8 to 4 ohm amplifier output and it was as if a veil was lifted from the music. In neither case did I realize that my system wasn’t optimized.

The soundstage can always only be as good as what’s on the recording, and a good setup should reveal huge differences between recordings. Lousy recording, lousy soundstage.

Phase coherency and time alignment of the drivers are significant contributors to good sound stage....kind of tough to make much progress if the speaker design isn’t up to snuff.

The room is a major part. Speaker position and listening position within the room are key areas to pay attention to. Every room is different, so experimentation is critical. You can follow good rule of thumb practices as a starting point, but use your ears to fine tune. Room treatment to address reflections, resonances, standing waves, and nodes, etc., can be done with carpet, drapes, and furniture, or aftermarket or DIY wall and ceiling treatments, and bass traps ... all can help tame the room. Its and art and science in itself.

Transparency of the system is also a significant factor...superb clarity reveals more of what’s on the recording. The whole system (speakers, amps, cables, crossovers, wires, connectors, preamps, phono stages, DACs, carts, TTs, tonearms, streamers, EQs, etc....everything in the path) has the potential to mask what’s available on the recording....all do to some degree. The difficult part is chasing down clarity in that entire path. Vibration damping and isolation of components is worth pursuing to optimize what you have. There’s no way around trial and error, and there will be many occasions of two steps forward, one step back (or vice-versa), but every step forward should reveal a bit more of what's on that recording. It’s a journey....enjoy!