As someone who owns both Coincident loudspeakers and AtmaSphere amplifiers, my opinion is that despite what is normally said, this isn't the best of matchups. Each of these components is on the more forward, lively, and engaging side, and I often find the combination can be a bit leaner than I prefer. I realize Israel Blume advertises that he uses AtmaSphere amplifiers, but he's also gone out of his way over the past decade to get into the amplifier business.
Personally, my Atma Spheres sound best with my older Fried (A/6 and, especially, Valhalla) loudspeakers, which present a more resistive load than the Coincidents. In fact, I've not heard the Atmas find a better companion. My Coincidents do best with transformer coupled tube amplifiers with more power than what most of their advertising goes towards, such as my Jadis. So, if you're leaning towards Coincident, I'd personally look into brands like AES, Air Tight, Audio Note, BAT, Cary, DeHavilland, Jadis, Manley, Music Reference, Quicksilver, and VAC.
Personally, my Atma Spheres sound best with my older Fried (A/6 and, especially, Valhalla) loudspeakers, which present a more resistive load than the Coincidents. In fact, I've not heard the Atmas find a better companion. My Coincidents do best with transformer coupled tube amplifiers with more power than what most of their advertising goes towards, such as my Jadis. So, if you're leaning towards Coincident, I'd personally look into brands like AES, Air Tight, Audio Note, BAT, Cary, DeHavilland, Jadis, Manley, Music Reference, Quicksilver, and VAC.