This is not as simple as just ’the room and speakers’ though they ARE very important in the chain.
You see the entire thing from the studio and mic’ing, the sound engineering, the pressing and onwards affects the stage. Let’s say you have a jazz combo where the musicians are close-mic’ed. Then more of the "soundstage" will be in the engineers’ and producer’s hands. They will control where an instrument appears in the "soundstage". Early Beatles recordings are great examples of this. If OTOH the mics are out in the room away from the artists, then you would get more of the studio’s acoustic signature in the recording with less specific placement other than perhaps left and right. Orchestral recordings done with only a couple of mics are excellent examples of this.
Do monaural recordings have "soundstage"? 😉
NOW we get to our "speakers and room" components. I have a pair of electrostatic speakers that are very sensitive to placement, especially as regards the soundstage. Contrary to what one would think, if I toe them inwards, the stage gets wider and less focused. As a consequence, the ’sweet spot’ though wider is slightly less satisfying. OTOH, if I toe them outwards a bit, the stage is very tightly focused at the cost of having a very narrow sweet spot. (And boy do I mean narrow!)
With regards to the influence by any components, other than speakers, I would suggest that your sources (LP, CD, Digital) which read and reproduce the recorded signals followed by your preamp would influence the sound stage. And finally, of least influence will be your amplification. Why? Good amplification will affect the quality of the reproduction in the chain (dynamics, frequency response, etc) but has little bearing on where an instrument will appear on the stage.
At the risk of causing controversy, I fail to see how a powercable might affect soundstage.
Happy listening.