Looking for the next level in imaging...

I misunderstood when I suggested the Larsen 9, because you’d mentioned the MBL’s. You’re looking for imaging, but those two are omnis. Sorry! I am intrigued by the Larsens (and MBLs, which I have heard) because they throw up a "wall of sound" that is more like live music but with less instrument and voice image specificity. Many of us, myself included, are conditioned by front-firing traditional speakers, though some would argue that the imaging and precise soundstaging they offer is an artifice, not realistic to live music. Of course, much recorded music, especially if recorded in the studio with many tracks combined at the soundboard and mixed for effect, is an artifice. Other than orchestral and chamber music, much of what I listen to probably wasn’t recorded live with all the musicians in studio together, playing as they would on stage in performance.

All that said, people who know and love the Larsens warn that the experience is quite different than front-firing speakers, and the AbSound review says that also. They have some advantages apparently, like being able to be placed up against the front wall without harming bass response, and are less affected by sidewall distance and room effects. 

I note that AbSound’s Jon Valin has as one of his reference speakers the top of the line MBLs with massive subwoofers. Big bucks!

Another direction is to get a quality subwoofer.  I just bought a REL S510, and it is an amazing improvement to my two channel system.

Suppose you buy a million dollar system and you don't like the sound.... what do you do then? I've had several systems over the years and it wasn't the most expensive that sounded the best. As for me, Martin Logan speakers sound really good.

I will second the Larsen and KEF suggestions. I have not heard the Larsens, but they are consistently reviewed well. And I have KEF Reference, the concentric design makes for a large sweet spot and very good imaging. 

Two specific ways to increase soundstage depth, as you seek.  First, increasing the distance of your speakers from the front wall can have a huge impact.  If this works in your room, it would be my first move.  Second, consider a tube based amplifier.  My McIntosh C22/MC275 do a much better job with depth than comparable solid state amps. 

Also, are you working with a dealer or other professional?  As noted above, this is a really complex process.  An hour or two from an experienced person might be well worth the expense