Hum... I agree that a well-executed amplifier and crossover is beneficial to the sound-stage, but I believe those benefits are more apparent in the actual staging of the instruments and players within the sound-stage.
The room itself, and the way in which the speakers are placed has more to do with the overall dimensions of that sound-stage. Speaker placement is the key to achieving a wide sound-stage. Then comes room treatments. I have heard some mid-fi gear that produces exceptionally wide and deep sound-stages, but at the same time poor definition within that sound-stage; and it is that definition ('realism") that we all strive for... Which entails much more than just dimensions...
The room itself, and the way in which the speakers are placed has more to do with the overall dimensions of that sound-stage. Speaker placement is the key to achieving a wide sound-stage. Then comes room treatments. I have heard some mid-fi gear that produces exceptionally wide and deep sound-stages, but at the same time poor definition within that sound-stage; and it is that definition ('realism") that we all strive for... Which entails much more than just dimensions...