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."
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."