Ralph, I’d still like to get your opinion on McIntosh amps with autoformers. Just in general, do you think they are a good sounding amp compared with other amps in their price ranges? Do they implement their autoformers well? Would they be a good choice for driving speakers with difficult impedance loads? Theoretically, of course. We all know that good sound depends on many factors in a given system.I was not aware that Mac was still making those; in the old days their autoformers worked quite well. But with those older amps I would not be asking them to drive anything much below 4 ohms.
The only thing difficult about the MLs is usually their impedance. Beyond that its my opinion that its a Bad Idea to make any amplifier work hard by making it drive a 'difficult load'. What happens is you get more distortion, usually of the type that make the resulting sound harsher and less detailed.
This is why I've recommended the ZERO so often in the past, as it allows the amplifier to drive an easier load.
I don't think the Macs have impedance taps below 4 ohms but usually they do employ a fair amount of negative feedback so they should work alright on ML loudspeakers if not pushed too hard.