Hi David, please accept my apologies if I wasn't clear in my previous post.
As for the Pass Lab users not using Pass Labs X amps instead of Pass Labs XA amps, every Thiel user I know that asked for guidance directly from Pass Labs has reported that Pass Labs has suggested that the X's would better serve Thiel's, with X250 and X350 with their various "." derivations most commonly recommended.
Yes, there are truly pure Class A amps that can double down while maintaining Class A all the while (the early Mark Levinson ML2 w/ 25 Watts output certainly jumps to mind). I was merely trying to make a generalized comment to a larger audience that might mistakenly believe that all amps that tout Class A, don't necessarily do so all the time. If I recall correctly the Aragon mono's dropped all Class A output below 8 Ohms despite being touted as pure Class A. I remember another manufacturer of a very highly regarded amp admitted when pressed that despite claims to the contrary, that his amps weren't really Class A and argued that it made no difference except in the market place perception. The current Pass Labs XA's aren't really pure Class A, as they provide extra Class AB Watts when power demands require it. To their their credit they only advertise the true Class A output, but unfortunately some leave thinking that these (advertised) relatively low output amps prove that extra power isn't necessary and/or that Class A is more powerful than Class AB.
Doubling the minimum recommended power is not my axiom. I've been at this for a few decades and it existed long before I became involved. Which is why I chose to use it previously. It is merely a long used generally accepted starting guide. I do believe that time has been kind to this guide, and though one might find less or more power might be required, and as difficult as it is find any specific guide I've found this one to be especially helpful as a general starting point. Heck, I can remember a time when 200 Watts was a broad brushed minimum recommendation for a serious system. That I think is an over simplification.
As for an amp being able to handle a 2 Ohm load, keep in mind this is more of a prerequisite with some Thiel's (especially at lower power outputs) if one cares a whit for frequency and amplitude linearity. Despite what might appear to be technically true, the 200 Watts that your Accuphase puts out at 2 Ohms is really not so different than 50 Watts into 8 Ohms. Which really isn't all that much. Now in a smaller rooms playing music without much in the way of dynamic contrast such as much small choral works or chamber music 50 Watts might be more than enough, but for realistic symphonic music in larger rooms it might be lacking. There's a reason Jim Thiel allowed his loudspeakers to handle such big power inputs, Many other speaker manufactures discourage such power, as their speakers can't handle it. Sure one can get sounds out of most any Thiel with even the most low budget low powered amplifiers, but if one wants all that Thiel's are capable of, then more high quality Watts are needed.
The halving of Class A output with impedance drops isn't really all that much of a problem. I just pointed it out because many attribute the sound of some amps due to their Class A output, when if fact it might be due to something else. Most of the time our speakers really don't require that much power. It's really only when things get loud do the speakers drink up copious Watts. But then the demands really ramp up. The thing is that as things get loud our ears aren't as sensitive to all the delicacies', that is until real distortions start to rear their ugliness. Personally I'd rather deal with an adequately powered Class AB amplifiers cross-over distortion than even the impending clipping of an underpowered Class A amp. Especially with solid state amplification. That is not to say I'm suggesting tubes with Thiel's, I don't. Though some do.
I do think we're really much more in agreement than not. I was not specifically trying to tell you what to do, or what to use, but rather to offer a more generalized response to a larger audience for your rather good question. I used to often say that we all hear differently, but I now realize that it's probably more correct to say we all listen differently. I don't like to argue with success; if your happy, enjoy!