As a former owner of the MG 12s, the 1.6s, and the 3.6s, I can tell you its going to be quite difficult to find a speaker that gives the magic you are looking for. As I now own a pair of Merlins which throw a great soundstage like the Maggies, they still don't have that dipole transparency. My advice would be as follows: First, try the 1.6s in the new room and see what you think. Its definitely a tight squeeze and the hard part will be getting them far enough from the front wall (the wall behind the speakers) to breath. Second, if they don't work in the smaller room, consider a modded pair of SMGAs. There is a startup company called Magnestand that makes modded SMGAs run by Peter Gunn over at the Planar Asylum on Audioasylum.com. I've heard these speakers on several occassions and they are fantastic. In my opinion, they have more PRAT than the 1.6s. I even liked them better than the 3.6s, though they clearly didn't have the amazing resolution of the ribbon tweeter. They are much smaller than the 1.6s, closer to the size of the MMGs. They integrate suberbly and they are, of course, Maggies so you won't be losing the love you have. They cost just a little more than a used pair of used 1.6s, somewhere in the range of $1200. Peter Gunn's craftsmanship is spectacular and his mods are innovative when it comes to performance (I've also heard unmodded SMGs and there is no comparison to the modded ones). If you want to email me privately, I can get you in contact with Mr. Gunn and he could advise you as to whether they would work in the small room (he's an honest guy and won't try to sell you anything that would be unuseable). Or, you can look him up on Audioasylum under his moniker, Peter Gunn. Third, if none of the above options work, I'd consider an open baffle speaker like the Alons, Nomad Ronins, or the Linkwitz Orions. Its just my opinion, but I think you would miss too much of the dipole magic that the Maggies give you with any other box speaker (based on the way you've described your affection for the 1.6s). Just my 2 cents.
Wish you the best of luck with whatever you choose.