I have tried many combinations, and I must say that the Atma pre / Atma M-60 is the absolute best to my ears and taste (there are many other great sounding pieces, so I'm not saying this IS the best, or the best for everybody - some might prefer the relative added warmth and texture of the Music Reference RM9 SE for example, or the seemingly limitless dynamics and drive of the CAT JL2, there is a lot of good gear out there - obviously the Joule gear is a must audition with Merlins - I did own the Joule LA-150MKII - very good indeed) - but for me, the Atma is an incredible match.
But, another combination I have been listening to is simply a great, great value and wonderful match - that is the Dodd Battery Preamp with the Pass/First Watt Aleph J. I know that Merlins are often thought to be a tube amp speaker, and they basically are and often sound their best with tubes, but the Dodd is an extremely good preamp, very quiet, dynamic and with the Amperex 6dj8 (1958)about as good as I have heard. Their 200 ohm output impedance makes them capable of driving almost any amp load, but in this case, with the Aleph J, a very easy load indeed, and very high 242 kohm!(unprecedented?) optimal for tube preamps in general. The Aleph J is easily driven by the Dodd. It is single-ended SS, Class A, only 30 watts (more than enough for the Merlins), 15db less negative feedback than the original Aleph 3 (which I owned and loved), low damping factor (20) which is good for the Merlins, and optimized for 8-16 ohm speakers. Known as a "tubey" amp in general, the combination is an under $4,000 combo that is mighty impressive with the Merlins - trouble is the Aleph J isn't made anymore, but can be found here from time to time for $1,200 - $1,500. Is it the best possible? proabably not, but for the price I think you will be very, very happy. I also used the Pass XA-30.5 that worked very well to, but at a higher cost. I think it might be a better overall amp (the best sounding SS amp ever?) with a wider range of speakers, but IMHO, the Aleph J is all you need with the Merlins.
P.S. I've tried the Dodd with the Atma M-60s. Of course it sounds very good, but I still prefer the Atma MP-3 pre with the amps.