A deeper more holographic soundstage.

Nice to see today's discussions are somehow more focused on improving room acoustic treatments than equipment upgrades. We are getting somewhere. To the unaware, pay attention, it may cost you some up front but you will save a bundle in the long run.

From what I can tell in my limited time here @baylinor, it is a serious uphill struggle.  Unfortunately it is easier to change a fuse or cable and claim a big improvement than to actually take the time, learn, learn some new skills, break dogma, and have a real, substantial, and long lasting improvement.  Once you solve those acoustics issues, then you get even more enjoyment from that upgraded hardware. If you don't address acoustics, then you top out early in performance. Some audiophiles keep "tweaking" in hopes of moving forward. Others just give up. 

From that I concluded that sometimes electronics do matter for sound stage even in the solid state category.

Electronic design quality always matter but most of the times way less than good controls of mechanical, electrical and acoustical dimension....

Wow. Reading all the comments really demonstrates there's a long way to go in audio before we all agree. It almost seems totally subjective and opinion driven sometimes. 

Some here overlook all recordings have reverb to some extent. You can listen to one speaker with a mono recording and still hear reverb.

Depth is nothing more than reverb done well. Done poorly and it's unconvincing that it's music being performed in room or venue. Live music performed in a church has depth. A piano in a room has depth. How BIG is the church and how big is the room?  Once you can sense that, you know your can be happy about your system's ability to reproduce depth. 

The answer to the OP: Phase. Do phase well (especially out of phase information) and you get "depth."