Many thanks for all your comments, which were very enlightening indeed. I too had a shiver running down my spine when I saw the innards of the Cortese for the first time. But the many enthusiastic comments about the sound of these creations by "Supratekkies" mostly from Down-Under, made me taking the plunge. I am sure, however, that I can still cancel my order, as it was only placed in November. I followed most of the links you supplied about the Atma-Sphere and "listened" to the descriptions. For me, a big plus is the all-XLR design, as both, my DAC and my Amps use balanced-only.
Now last night, two new listings on USAudiomart came to my attention, namely for the LAMM LL2.1 DELUXE Preamplifier and its corresponding phono stage, the LP2 deluxe, both at a reasonable asking price compared to new.These are rarely offered on the used market (always a good sign), and I read great things about the Lamm designs and how they "sound" (they apparently have no sound signature of their own), and now I am afraid I am going down the well-known rabbit hole. Just to give you an idea, how this "no sound of its own" statement appeals to me: last October I almost bought the PASS XP25 phono preamp; the seller was kind enough, however, to send it to me for trial. I had only heard great things about this instrument, and I do know Nelson Pass personally. But here it comes: I did not like it a bit. The sound coming out of my LX521 speakers was bombastic, no matter how I fine-tuned the many parameters, and - even more disturbing - the sound stage appeared in front of my speakers, defeating the purpose of spatial stacking that open-baffle designs offer (the LX521.4 create a true "phantom-image" deep into my living room, especially on solo piano). I listened to that unit for two weeks almost every day, trying all possible setting permutations (a great forte of the XP25!): I really WANTED to like it, and then I sent it back! MY verdict: it's super for Credence Clearwater, but not for Callas.
Hence my asking for help once more: of these three options, which one would you pick, if possible out of your own listening experience? And yes, the Lamms are single ended, I know.