Recommended Speaker List for Atma-Sphere OTL Amplifiers.

I have the M60s and MP3 and use Vandersteen Quatros. Sounds incredible with no zeros needed.

I use a pair of John Wolf's T3.3 Classic Audio Loudspeakers  with the field coil option with my Novacron's. 

The Atma-Spheres are amazingly transparent with a huge sound stage. I would go with speakers capable of producing a huge sound stage and ones that are transparent. 

I have used the M60's and the MP-3 with the older model Wilson Benesch Curves. Great sound. There is a pair of Audiogon right now.

At the risk of stating the obvious, they should have a high, relatively flat impedence curve for the most part, although as others noted, they are reported to mate well with Quads.  Also Soundlabs and Magnapans, IIRC.  I have used them successfully with Merlins, Hornings, and now with a DIY pair of open baffles with field coil mid/tweet and conventional mid/low bass units.  From personal experience, if you have the room, they are fantastic with the Classic Audio speakers, being able to reproduce live SPL rock music in a very large room with the M60s..  If you want to get an opinion about how they mate with a particular speaker, you should ping Ralph (Atmasphere screen name), if he doesn't show up here on his own.  You will get an honest opinion with, IMO, no marketing hype. 

I am well aware of the smaller inconvenience of owning OTL gear but in my honest opinion for this level of quality in enjoyment I am more then willing to compromise. Once the match of the speaker and amplifier is complete all you experience is pure magical bliss!

The T1.5 Classic Audio Loudspeakers are excellent and magical theirs nothing like it. Its just flows with music in a emotional way that sparks your deepest feelings so easily, I feel like I'm transported somewhere else. 

The speakers are full field coil. These are a keeper I would never part with them. Mines are paired with the New Atma-Sphere Amplifiers "Nirvana". A Super Regulated OTL Amps LOL The best Atma has developed till date I guess.

The OTL amps have been a revelation. I was more in to SET and certain push pull class A design but never experience this form of lucid feeling from a sound system.

Its going to be hard to find a speaker that can perform like a Classic Audio Field coil but in a smaller and less expensive package and designed for smaller rooms.

I have been considering smaller horn speakers or Single wider-band drivers too. Just not settle down yet and need to go out and listen to some of the manufactures that are based in the EU.

My ultimate goal was to build a smaller system with another set of Atma-sphere gears this time with the MP-3/MA60. Once you go OTL you cant go back :-)  Everything else just sounds slower and less transparent. I cant seem to enjoy my previous gear (for second system) and thus had to sell some of them off.