What you heard is a subjective opinion by a person who has not done a careful blind test. Therefore the premise that one amp has a wider soundstage is suspect.
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?