@bobster50
There is a pretty significant difference between the MA8950 which is a transformer coupled (Autoformer) design versus the MA252 and 352 which are direct coupled. The vast majority of tube amps are transformer coupled due to the fact that high output impedance necessitates it. However, Solid state amplifiers don't suffer the same challenge and rarely employ output transformers. To my knowledge, McIntosh is the only company currently producing them. The advantage to having an output transformer is that the design can be optimize for one consistent, predictable impedance. The different taps represent longer windings, but all speakers (taps) will see the amp's potential output, not just lower impedance options. There are downsides - a large transformer (lots of copper) in the signal path, weight, and especially cost. McIntosh produces Autoformer in house and they're good at it.
While I will stop way-short of saying that transformer coupled solid state amplifiers are inherently better than direct coupled designs, McIntosh has honed the craft which is why all of their top solid-state models employ it. And since many people love tube amps and part of what you're hearing is the quality of the output transformer, it stands to reason that Autoformer amps may share a bit in common sonically with their tube counterparts.
To my ear, recent Autoformer McIntosh amps share the quality of being somewhat smooth sounding. My MC462 has a mild bottom-up presentation, it's dead-quiet and it's utterly smooth across the entire frequency spectrum.
So, long story short - The MA8950 doesn't possess the mildly dryish qualities I've heard from the MA252 and 352. It sounds more like the 462 to me and I think most who have listened to enough Mac gear would probably agree.
As for tubes on "harder-to-drive speakers," there is a consensus that they can't do it, but I've been surprised in the past. The Forte III, IMO, wants current. The little Maggie 1.7, while lower in sensitivity and impedance, is different. I once drove a pair of Martin Logan Aerius i with a Canary 300B amp and was surprised by how well it worked. I also had a dealer near me who made a career of driving Maggies with tube amps. He was quite "eclectic" but also brilliant. People in the industry were hard on him, in part because he was different. But I heard a few of his systems personally and I think that if others had, they may have struck a different tone.
