Benchmark ABH2 compared to Merrill Element Series and other ultra high end amps

The AHB2 is a special amp given the right load. It is not a good amp for ESLs. As soundhound mentioned ESL's drop their impedance as the frequency increases. Even mono strapped AHB2's  do not do well. However with an 8 ohm or higher, efficient speaker say like a Klipsch the little amps kick ass. They are priced lower because Benchmark makes professional equipment and the market is priced differently. They also really have their act together. I have their ADC and it is a little jewel. Beautifully constructed. I have no trouble recommending their equipment under the right circumstances. Don't let the price fool you. Benchmark stuff is as well made as anything out there. 
I have never been close to a Merrill amp. 
As far as ESLs go, and I have been using them for decades the JC 1 is very hard to beat. They make my stats thunder. Pass amps do very well.
The best may be Atma Sphere MA 2s.
 I am not an ML fan. Curving a panel is a silly idea and the man who designed them, Roger Sanders agrees. As far as Hybrid ESLs go Roger makes the best and they are very easy to live with. His amps also do a fine job driving ESLs. Sound Labs currently makes the best ESLs available by a fair margin. But, they are no compromise speakers and even the small ones will dominate a room. The big ones own the room. They are huge but boy are they special. They were using JC 1's to demo their speakers.