I did have some AMTs crossed at 7K in the back room on top of some Altec 416s but recently got some Aristocrats with EV triax which I listen to back here for now.

For grins, chuckles and personal edification I decided to stack the AMTs. Since I have them crossed at 10K I can't tell you how low you might take them. Also 1 pair has original diapragms and 1 pair new. I believe the new can take lower Hz but to my ears the old are a bit better at the top. Slightly different materials I guess.

I still have them stacked because I just haven't felt like getting the soldering rig in there and changing things back. My opinion is that the highs have become a bit sharper, or as I told a friend,"Like breaking glass."

I don't know if it is because there is twice as much area for producing highs, using 2 different diaphragms or what. I am not really answering your question because this isn't really an array and the bottom ones are head high sitting on boxes but there has not been any kind of improvement in presence, placement, soundstaging and to me just a tad bit of too much brightness.

I went to T.H.E. Show in Las Vegas a couple of months ago and listened to the new Oscar Heils which are 2 ways with the dipole AMT on top. I wasn't impressed. The AMT is smaller and the rest of the speaker seemed a bit slow, so it was a bit muddy.

Since these are dipoles and a lot of what you hear is bounced off the wall(s), I don't know if a stack rising from the floor would give you better imaging than just a pair. If you want to play around with these I would suggest that you limit the bandwidth on the ones close to the floor to mids and the ones on top to highs. These do have great mids, but seem to be best used only as tweeters. The diapragm life should be greater by not trying to get over 19Khz range out of them too.

I use a 300B SET stereo amp with a pair of isobaric subs running on SS for bass. AMTs are faster than ribbons, so matching drivers for speed as well as efficiency is important.