As far as sound quality, the digital data is the same, and the analog output of MOST DACs (including whatever is built into your computer or phone) are already better than human hearing. (I had once a soundcard that made noise when the hard drive was accessed, but that's not common and it's a specific and easily identifiable problem.)
You may have other reasons to "upgrade" but not for sound quality unless you've got some kind of problem. Different speakers (or headphones) will ALWAYS sound different (better or worse). EQ can obviously change the sound. Of course a higher-power amplifier can go louder, if your speakers can take it. Or, I like to use the "hall" or "theater" setting on my AVR for some delayed reverb in the rear speakers and the "feel" of a bigger room.
"Detail" isn't really defined. Personally, I'd associate more detail with boosted high frequencies, but Dan Clark (headphone manufacturer) says that headphones with more distortion are often described as "detailed"!!!
Soundstage mostly comes from the recording, but your brain is also involved since an illusion with the sound really coming from a pair of speakers.
The electronics don't affect soundstage unless you have a "blend" or balance control or something like that.
Floyd Toole says:
But speakers and room acoustics do contribute. Dipole and omnidirectional speakers create more "immersion" and I believe a bigger but less precise soundstage.
