IMHO, clarity is one of the most significant contributors to soundstage. If your speakers have good phase coherency, and are mated with an amp with good clarity, you should get a good soundstage if properly setup.
Why do some amplifiers throw a bigger soundstage than others?
Was watching a YouTube video comparing two Excellent class A amplifiers . the reviewer preferred, the one which threw a wider soundstage with the same set of speakers. Specified channel separation in db iis about the same in all quality amplifiers., so why does this happen?