Creating a Large Sound Stage

Speaker placement and listener placement are the most important elements in good soundstaging.  Whether that gets you to sound appearing beyond the speakers is then a matter of whether the recording has such information that your system is capable of delivering.  
Some recordings deliberately manipulate phasing and timing of the signal to generate such imaging, but, how effective this is depends on how well you have set up your speakers and whether or not your speaker design messes up such timing cues.  An example of a recording utilizing such manipulation heavily is Roger Water’s “Amused to Death.”  
Placing speakers as far as possible from reflecting surfaces and not having such surfaces between the speaker and listening position helps (i.e., no coffee table in front of your seat).  Adjusting toe-in is also important—the more toe-in the stronger and better defined will be the center image but the sense of image width will suffer; you need to find the right compromise.

Creating a Large Sound Stage

Constant Directivity Horns!

Mike

Everything matters, but some speakers just image and throw off a big 3D soundstage better than others so it greatly starts with that, and placing speakers too close to walls squashes subtle things like reverb trails that contribute greatly to soundstage size and sense of space.  So everything matters, but starting with speakers that have these qualities and positioning them properly is a huge part of it, and of course room/treatments also come into play. Just my $0.02 FWIW. 

It is necessary to control the room acoustically...

Any relatively good pieces of gear can be used.

The main factor is understanding of acoustic concepts and how to use them and modifying them...

Reflections/diffusion/absorption devices in balance and well located...

We can use DSP or mechanical devices to modify  the  speakers behaviour in the room in relation to a listener location...

We must take control of the pressure zones of the room ( i myself used Helmholtz resonators grid but it is unesthetical and impractical for most people then you must use DSP ) 

The most important concepts are : Timbre with Reflections/diffusion/absorption ratio and ASW/LV ratio ...If you dont understand what they are you will buy gear upgrades till your death without never creating an immersive soundfield... 

The gear pieces must be synergetical, and relatively good pieces (at any price); the focus on the gear impact made by most  hide the essential : acoustics concepts and parameters  controls including psycho-acoustics...

My low cost system in my first dedicated room gave me a total immersive soundfield completely out of the speakers plane, including my listening position, with in some recording, voices speaking to one of my ears and an orchestra playing behind the speakers at the same time ...Thanks to acoustics basic understanding...(It could have been improved only by Choueiri filters  but i was happy as it was) 

This experience had nothing to do with my gear design value or power which was good but low cost: vintage speakers (mission Cyrus) and amplifier (Sansui Au 7700), low cost dac (SPS nos) 

The room, how the speakers are placed in a room, and the speaker’s dispersion character. 

Based on my experience of conducting level-matched comparisons, upstream components have little impact on soundstage width. The exception is tubes vs solid state, where the former can create a slightly more expansive soundstage, probably due to the harmonics.