Since the jumpers used in the Atma amplifiers to reduce gain do reduce gain by converting the voltage amplifier stage from a dual-differential cascode to a simpler dual-differential topology, it is entirely possible that the signal to noise ratio might well go UP rather than down with vs without the jumpers. Cascodes have a pretty darn good signal to noise ratio. But in either case, there would likely be no problem except possibly with ridiculously efficient speakers, i.e., >105db. (I chose a number out of thin air.)
On the subject of speaker efficiency: I think the benefits of efficiency, if you define that as 90 or 92db and up, are huge, provided the speaker is otherwise well designed and pleasing to its owner. I do not care for much less efficient speakers, if they come by their inefficiency by virtue of a multi-way complex crossover, regardless of how huge and powerful the driving amplifier may be. I don't find that huge power can overcome the sluggish behavior of such speakers. On the other hand, horns are not my cup of tea, either. They invariably sound great for the first 15 minutes, however. This is purely and only my own opinion.
