question of soundstage

I had a Krell FPB 600 hooked up to an ARC Ref 6 SE. I then upgraded my Krell to the ARC Ref 750s. Huge difference in sound stage. Soundstage definitely comes from the amp imo. 

different tubes have different characteristics even the same numbered ones. For example, the Sylvania Chrome Domes are not as side as the Linlai 6SN7 tubes in our preamp.  .Same goes for preamp vs amplifiers.

....and I've been subject to the delusion(s) of 'sound stage' (the perceived width x 'location(s) of performers/instruments') is more a function and/or 'synergy' 'twixt speaker types/room placement/room response...And the 'mixdown' of the applied musical selection...

Whereas, the electronics and the medium from which the selection is applied is (or ought to be) +/- a 'non-participant'...

I'm willing to accept and allow a %tage for LP's and 'physical media' of it's type....*s*

Devils' Advocate Hour.... ;)

Your equipment, cables, et all....ought NOT to add 'color' or 'warmth', which has already been and chided over as being terribly....subjective...*gasp!*L*

Oh....beg y'all's pardons....

You're referring to A amps....

As the woman was prone to mention after a rant or dozen....

"Never mind..."

I will preface my response by saying I am not an audio engineer and do not have experience with your equipment.  I will present my experience in the pursuit of sound stage as it relates to electronics.  Another preface is that the speakers, room, wiring and power  quality also apply.  From the perspective of electronics the factors that affect sound stage are channel separation/cross-talk, noise, detail retrieval, and macro/micro-dynamic retrieval.  Modern electronics have excellent channel separation.  I focus on detail retrieval and micro-dynamic retrieval and its impact on soundstage when evaluating new electronics.  I listen for how the equipment produces secondary harmonics and decay, leading edge reproduction, detail of the micro dynamics during decay, background noise, imaging and stage.  I have a few test tracks I use.  As an example, when I upgraded from my well maintained ‘97 vintage pre and power amp to my current integrated amp the improvements in these areas created a sound stage that was much improved and realistic.  So you cannot generalize that your tube amp will give a better sound stage than your solid state.  Your solid state may just be performing better than your tubes in the performance areas I mentioned. I believe my integrated amp performs as good if not better than most tube products I have auditioned, noting that I personally  am bias to the cooler clarity of well designed solid state vs tube equipment.