We have a number of customers using the RM-200 with their ML speakers. It's an excellent amp for the job. OTLs can also sound great, if Atma-Sphere I would recommend the MA-1 which is 100 watts. I'd recommend putting the autoformer in between the amp and speaker, but it may not be necessary. Ralph could advise as well.
There is some debate on whether the Berning patent for his design and that is now used in the LTA amps is actually an OTL circuit. IIRC there is a high frequency transformer that follows the tubes in the circuit. Therefore, some feel that technically it can't be an OTL and I believe Berning more accurately refers to the design as Zero hysteresis since that high frequency transformer does not behave like a traditional output transformer. So the other side of the argument is if it doesn't behave as an output transformer it is still an OTL (output transformer less).
There is some debate on whether the Berning patent for his design and that is now used in the LTA amps is actually an OTL circuit. IIRC there is a high frequency transformer that follows the tubes in the circuit. Therefore, some feel that technically it can't be an OTL and I believe Berning more accurately refers to the design as Zero hysteresis since that high frequency transformer does not behave like a traditional output transformer. So the other side of the argument is if it doesn't behave as an output transformer it is still an OTL (output transformer less).