Too bad more audiophiles don’t investigate the suggestion of @ticat, myself, and a few others, and look into the Eminent Technology LFT-8b. A planar-magnetic loudspeaker, in some ways very much like the Magnepan, but in other ways dissimilar.
The LFT-8b is more like an electrostatic than are Maggies, in both sound and power amp appropriateness. No offense to either Magnepan or owners of their outstanding loudspeakers (I have owned four pair, one currently). But if you want a planar loudspeaker that will mate with the Atma-Sphere M-60 (or generally any tube amp), the LFT-8b is a great option. It’s modulus-of-impedance is a very even 8 ohms, the p-m panel itself (which sits atop a sealed 8" dynamic woofer for the reproduction of 180Hz down, via a second set of binding posts) an almost ruler-flat 11 ohm load, ideal for all tube amps, none more so than an OTL such as the Atma-Spheres (with which I am very familiar, having used a pair of M-60’s with my QUAD ESL’s, a/k/a 57’s).
Despite very positive reviews in The Absolute Sound, Hi-Fi Choice, Hi-Fi World, Hi-Fi Pig, Positive feedback, and from Harry Weisfeld of VPI (who declared the LFT-8b to provide the best midrange reproduction of any loudspeaker he has ever heard. The ET LFT driver reproduces 180Hz to 10kHz, with NO CROSSOVER!), U.S.A. audiophiles continue to ignore the best value loudspeaker (imo) of any on the market.
Part of that blame can be attributed to the low number of Eminent Technology dealers (which pales in comparison to those of Magnepan), but E-T will ship you a pair to audition in your system. Some E-T owners prefer the LFT-8b to not only the Magnepan MG-1.7i (I have heard both---it’s not even close), but also the MG3.7i, which retails for more than twice the price of the LFT-8b.
I expect this post will be ignored as have been all like it in the past. It’s your loss, not mine ;-) .