How Do Amps Affect Soundstage?

@zazouswing exactly the way to look at it.  All the goodness is in the recording and the question is, can your system reproduce it without degrading it.  A system doesn't add anything (good).

Jerry

For example, if you put an amp in the middle of the soundstage you could trip over it. That is one way how an amp affects the soundstage.

Allow me to think out loud so to speak...

Lower frequencies have longer sound waves and higher frequencies have shorter sound waves.  This is why the location of tweeters is critical to the listening experience and subwoofers can be strategically places in the room.  It seems reasonable to me that there must be frequencies somewhere in the mid range where the there's a shift away from directionality.  Maybe an amplifiers (or any pieces of gear) ability to produce these frequencies is what impacts the sound stage.  The relative timing from the two speakers is what creates the stereo sound/soundstage.  I'm thinking that any degradation in these frequencies could negatively affect the timing leading to a more directional sound which would be expected to shrink the perceived soundstage.

"I'm not that technically strong on audio yet, so please refrain from mockery on this...."

I've been on Audiogon for just a few months.  This is one of the saddest comments I've read. 

This is an expensive hobby.  We are much more financially successful than most people.  And probably much better educated.  We should be better than this, welcoming new people not making them fell stupid. 

I've all tubes. I do find that they have a more pronounced three dimensional soundstage. It could be that they simply have a lower noise floor—allowing the tiny signals necessary for the most nuanced sound cues through. It could also be that the glass picks up sound waves which causes a slight reverberation giving the music a more echoic perception. 

Monoblocs sound better because there is no cross-modulation between channels. In other words, you get better stereo separation.