Pass x250.8 vs Boulder 850 vs Spectral DMA250

"Here are just some that look to have bi-polar output transistors as they seem to come close to doubling wattage for every halving of load impedance from 8ohm 4ohm 2ohm.
I dug these out of Stereophile's test results they seem to do the current needed for the heavy load in the bass your speakers have, but as for the sound it's up to you to decide"

Bipolar transistors are not the only option. There's plenty of amps that don't use bipolars that will be able to drive the op's speakers. An amp is the sum of its parts put together by a designer that knows what they are doing. I don't know if you have ever heard any of the 3 amps the OP mentioned, but the Pass and Boulder will will drive the SF's just as well as the Spectral, if not better.

@Zd542 definitively yes. BJTs that George suggest are valid and with no doubt they potentially drive the SF at their best. But the sound pressure I can drive these speakers is for a normal listening room (50sqmt in this case) so the power request can be managed also by Bouldes or Pass.

If you know the SF Elipsa Red or Stradivari sound, they have a wonderful bass but it needs a lot of control.

First I was oriented to pure Class-A amplifiers but when I realized that most of them are monos -and I don't have space for two amps- I was looking elsewhere.
From the George list I guess the only amp I can ask for a test is the Ayre.

Sure I will test all initial three.

My dentist plays with the first generation Amati's. He uses Krell amps of about 7 years old. The sound is stunning. I heard these also with ML. It sounded dead, without emotion. Even depth was of a very low level. Yes SF needs power and speed, because SF does not use units with the best response. You need a lot of power and speed to solve this limitation. But....also you need emotion. It is easy to get a clinical sound out of a SF. I love classical music with SF. I think SF will be my new brand in speakers I will start to sell. I will use SF for it's design and for the options of more expensive speakers.

@Bo1972 It is not a mistery that Franco Serblin (r.i.p.) tested its own products, in the first instance, with Spectral, his personal setup, and (maybe not confirmed) Krell stuff.

In 16 years of time I heard many spectral demos. There was
not even one time that it gave me a smile on my face. What I
said earlier; in a few seconds I can hear to all different
parts which need to be there. There is a lot missing with
Spectral in my personal opinion. In a few demos I really
liked the speed and depth. But.....other things were still
missing. For me this is incomplete. I don't want it. I prefer
and even demand a small and realistic intimate sound. I never
heard any Spectral do this as I want it to be. I hate
classical music played by spectral. It irritated me a few
times. I asked the dealer;do you think a violin sounds like
this? I said: it sound like a clinical violin. That is not
how it sounds in real. This brand I also not even want for
free. Pass labs is superior in emotion compared to Spectral.