From whence does Sound Stage come?

What drew me back to this hobby after dabbling in High School, was listening to a friend’s system, in a room over his garage filled with over-stuffed furniture, at least seven different amplifiers and twice that many speakers. What was new to me was a room literally filled with sound, and I couldn’t tell where it was coming from. I climbed over the furniture and put my ear to speaker after speaker, but I was never able to locate the source of the sound. It was a wonderful, awe-filled, experience.

Fast forward to the present. I have now built several systems, in different rooms, with different components. Sometimes I get a ‘sound stage’ where the speakers disappear, sometimes I don’t. I have been told that getting the speakers to disappear is all a matter of placement in the room: “Give me your room dimensions; and I’ll tell you where to place your speakers.” But I can tell you, some speakers disappear, and some speakers announce their presence with every note. I have had odd staging where a particular sound appeared un-naturally at the wrong place (like a cymbal hit at my feet); only to have the issue resolved to a more coherent shape with an upgrade to the analog output stage of the DAC. I have had a decent sound stage cast by a particular pair of speakers, only to have it destroyed with the use of a sub-par power amplifier. I’ve heard reviewers and designers talk about how their component offers sound stage depth as well as width (depth seems to be more difficult to achieve). And then there is the old canard about how tube amps present a ‘halo graphic’ sound stage. I can detail the equipment configurations that have I have put together that succeeded or failed at the goal of presenting a great sound stage, but I’m trying to ask a general question, I am not a bot, and I’m not seeking help with a particular configuration, just help on developing a strategy to tackle the issue of sound stage and imaging of instruments within it. 
I will say that the best sounding solutions I have developed thus far both involved a Schiit Yggdrasil (now at ‘Less-is-More) into a SS McIntosh C100 (circa 1992) and either a tube Rogue ‘Stereo 100’ or a SS McIntosh MC252 power amp powering either the Warfedale W70E or B&W 801 Matrix speakers. If I substitute different amps, speakers, preamp, or DAC, the pyramid crumbles and I start hearing two speakers again; I lose my ‘sound stage,’ which is really concerning (to me). Anyone with more than two years into this hobby is qualified to address this question. I need some help, I can’t just keep throwing equipment (and money) at this issue. Any ideas?