I think you're on the right track. Sure you can put better electronics in front of them and the B&Ws will probably throw a better image than they do currently, but they will never image as well as the Proacs you heard.
I had a similar watershed moment in terms of holographic imaging when I heard Thiels driven by a Pass Aleph 3 and Bryston preamp over 10 years ago. I have found time/phase coherent speakers excel in this regard, including Thiel, Vandersteen, Green Mountain Audio, etc. But there are many others that do very well in this area as well such as Joseph Audio, Silverline, Totem, and Audio Physics among others.
In your price range new I'd look at the Silverline Minuets, Ascend Acoustics Sierra 1, and the Epos M5. If you go used it opens up virtually all the manufacturers listed above and more. I'd bet any of them installed in your current system would improve sonic holography a good bit and will blow the B&Ws out of the water with better electronics as funds allow.
An important point is that even speakers that have the ability to cast a believable 3D image will be limited if not given the necessary space to breathe. You've probably already addressed this, but unless you pull the speakers at least a few feet out from the back wall (and preferably more) the imaging won't physically appear as convincingly. Many cables/interconnects (especially interconnects) will also limit the holographic imaging ability, and I would doubt the Monsters are doing you any favors in this regard. I've found Stereovox interconnects do very well with sorting out a believably dimensional image as I'm sure some of the others mentioned do too.
Hope this at least gave you some ideas, and best of luck.
