Ryan,
Great question about what I am looking for in a speaker.
I cannot put that into words - but I can try.
I want the speakers to provide accurate sound.
I should be able to close my eyes and think the music is being played live.
Something like that.
I know what you're saying, but what you describe is more of function of how the speaker images in a room. The ability for a speaker to disappear and leave nothing but an illusion of space ... that illusion where the vocals are centered in front of you and behind the plane of the speakers, with all the other instruments scattered around from left to right, and front to back.
Imaging is very room dependant. The keys to getting a deep/wide and firm stage is having the speakers out from the rear walls at least 3 feet (more if possible), and at least a few feet from sides. Also you want a somewhat symetrical room layout. For treatments, the most important parts are plenty of damping on the rear wall behind the speakers - a bunch of heavy curtains are ideal. And treatments at the first reflection points.
I'm just laying that out as a pre-requisite to proper imaging, so assuming you have that covered, let's talk about the speakers more.
What sort of music do you most want to sound realistic and live? Jazz, amplified rock, acoustic, orchestral? And is what you listen too typically recorded well?
Accurate is a subjective term, to define it you'd have to talk to the recording engineer for each separate recording. If you ask somebody on the forum what accurate means in a speaker, they'll probably tell you a flat FR curve, but that tells you very little - two speakers can measure nearly identically on-axis and sound incredibly different. For this I'm interested in what sound you're looking for. To break it down there are:
Musical - speakers that have a warm soothing character, that never sound harsh even on bad recordings, but might lack the ability to wring out every last detail in the reording
Analytical - speakers that have a more sterile presentation, more crisp and defined notes. Speakers that make you hear things in recording you've never heard before, but can be painful on bad recordings. These are the speakers that can wring out all the details in the recording, good or bad
So which camp would you see yourself in? Or somewhere in the middle?