I heard the Sanders at 2 locations way back when. I had typical MTM cone speakers back then, not Apogees, so my memory is in comparison to those MTM's. Both Sanders were in NY apartments, one fairly small and somewhat nearfield and the other in a slightly larger room (remember ... NY apartments). The nearfield experience was what many will report - head locked in a vice, good space and transparency. The larger room (Wes Benders) allowed us to play them louder and gave them more room to breathe. The soundstage was still very much a one person thing and the dynamics were better, though not as big as many cone speakers.
Many years later I had the chance to obtain some Apogee Caliper Sig's which were in dire need of repair. I did what I could and upgraded the crossover on my own too. They were a great speaker in my room, but the ribbons had that dreaded buzz so I couldn't crank them.
I sold those to someone and upgraded to Duetta Sig's which I pulled the crossover out of and upgraded into a separate box with potted coils and upgraded caps (danm, there's a lot of caps in there) and wire but kept the aluminum ribbons intact. They are still in great shape. These have the reputation of being a one person speaker as well as the Sanders, and you do get the best sound from that one seat, but even sitting to the side they shine and are more dynamic than the Sanders (from memory). I will never part with these. They are by far the best speaker I've had in my room, driven with a Mccormack DNA500 arc welder of an amp and a tubed front end. I use stereo REL subs and have a crossover cutoff on the bottom end of the Apogees at about 75Hz to help preserve that fragile bass ribbon. You won't have that need if you have fully upgraded Apogees, which are faster still and more dynamic. Yes, I've heard those many times at a friends place.
I will say, you need tubes somewhere in that chain to assist with the bloom, and setup has to be within 1/4" of perfect. Yes, they are finicky but isn't that half the fun ... playing with the setup to perfect it?
If you want more info on Apogee vs Sanders I suggest you contact Wes Bender who was a Sanders rep long ago.