Why do some amplifiers throw a bigger soundstage than others?

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.

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.

@jasonbourne71 

Right on.