Amps that work well with Merlins:
The top two positions are both occupied by OTLs. It is not coincidence that Merlin shows with Joule Electra at shows. The other OTL is Atma-Sphere, usually the M-60. There are more M-60 owners with Merlin than any other speaker.
The speakers were literally designed to work well with OTLs.
Next is the ARS, likely followed by the RM-9 or RM-100.
The speakers are tube-friendly but you want a little power, 60 watts is a good minimum. For that reason most SETs are out unless you are in a very small and lively room.
The speakers play nice with transistors but you aren't going to hear what the speaker does with them...