How Do Amps Affect Soundstage?

I have heard very good sound staging with otherwise bad sound. Distortion will not always reduce the size, width, and depth of the sound stage, although it usually doesn't help. It might sometimes, for some people. I've had the soundstage pop into place with a little equalization, proper application of a house curve. For the sound stage of a 2 channel, 2 speaker system, there's abundant  interaural crosstalk that is unnatural and difficult for the ear/brain to interpret consistently. How that gets interpreted depends on a lot of factors and can make it tricky to get a good soundstage, which may happen for one person and not another listening to the same system in the same sweet spot.  Addressing interaural crosstalk means doing something beyond the orthodox 2 speaker listening triangle. My experience is that there's a hard upper limit to what can be done with just two speakers in terms of sound stage. You may find something that works really well for you. Some things that seem to always help are well matched speakers and amp channels - as close to identical as possible, perfectly level matched. Good off axis performance of the speaker can also help, and dealing with early reflections by carefully placing the speakers and judicious application of room acoustics. I think it generally helps to have a decent distance from the speaker to adjacent wall surface, which will provide some delay and attenuation of early reflections. The 2 speaker listening triangle is a delicate and fussy thing that presents the ear/brain with a signal that has inconsistencies in terms of soundstage and tone that can at best be mitigated.

Amps do affect the sound stage quite a bit.    I have found overall noise is a significant factor in soundstage width and depth.  Quieter your components usually contribute to a larger, more impressive sound stage. 

I have done my own listening test using up to 4 different Amps - using the exact same equipment, locations, music and just switching Amps.  Yes Amps can make a huge difference.  My Brystons 4BSST series produced the tightest most stable  imaging and sound stage.  They also had lightening fast response and slam thru my Maggie 3.7i.  My BAT 655SE produced deeper and better definted bass and seemed to have endless power.  In most ways the BAT are more pleasant to listen too, but they just don't hold imaging like the 4BSST.  I'm just guessing here and I'd love to know if lower frequencies maybe don't give us the same imaging clues as higher frequencies.  Maybe the BAT Amp's low frequencies emphasis drowns out the mids and highs that are more important for imaging.  

Yes some amps comes close to getting most right and they are generally more expensive. My final test would be how musical they sound and how enjoyable and involving they are