Are Pass Labs amps probably the best ever you can buy ?

I'm a huge fan of Pass, but I don't think their ideal for everybody. They may be some of the best built amps, but the best sounding amps is a more personal matter. There's a huge difference between his single ended Aleph series and something like the XA25. Same goes for the J2 and F7. 

"At Pass we build amplifiers with excessive output stages, huge heat sinks and massive power supplies. We use the highest quality components in simple linear topologies, assembled and tested with great care in Auburn, California. They measure well and sound great. They are heavy, reliable and expensive."
In my opinion, the only way to go is class A and I'm not sure anybody does it as well as Nelson Pass. Beyond that, Nelson is just an excellent human being that embraces a great life philosophy. I think the thing that makes Nelson such a great guy and engineer is that he finds fulfillment and joy in giving and humbly receives new ideas and approaches to things through that process of giving and interacting with his customers, fans, and DIY'ers. That guy has taught me a lot. His followers have taught me a lot. 
Best amps there are? Tough question. Are his mainstream amps everyone's cup of tea? No. The guy readily admits that some speakers pose problems for amps that he doesn't waste time worrying about. On the other hand, he's designed some amps that are ideal for very unusual speakers. They're all very well built. He puts a very high priority on his designs being very stable and reliable. I love my F5. I haven't heard anything yet that compares to it and there's definitely room for improvement. But I'm sure it's not for everyone. 

@wolf_garcia 

Take a look at the SIT3. It uses 2 complementary input JFETs to drive an autoformer for voltage gain followed by a single power JFET output actively biased by a MOSFET constant current source. A real damping factor, 200kR input impedance, and a near double of it's output into 4 ohms...it's a real amp with real triodic response curves that makes real power. 

@almarg 
I just crunched the numbers on Wolf's speakers assuming a typical room size and speaker placement. He should only require about 9 watts to get up over 101dB at 14 feet away. That figures out to about 9.5dB of gain. The SIT3 would work. It wouldn't work for me though. I need about 3dB of pre-amp gain to get where I want to be with the F5 at it's 15.5dB. It's easy enough to fix that if I wanted to. Getting it up around 19 is a matter of swapping 4 resistors. Most people do make that change when running 32V rails. I didn't. 

Dowto1000,

May I introduce you to the Pass SIT by SemiSouth, a power JFET with triodic curves and massively more gain than a triode, less distortion, that can directly drive a load without a transformer. 

There certainly ways of getting the qualities of a triode out of solid state devices. It's just a question of choosing the right devices and topology. 

Dowto1000

Here's a list of Pass amps with no feedback...
F1, F1J, F2, F2J, F4, M2, SIT1, SIT2, SIT3.

Those are all amps that will drive an actual speaker load. I'm not sure you could even call a .3 watt amplifier a "flea power" amp. Perhaps "microbe power" amp would be more accurate. I really don't think the ACA should be considered much of a measure of what characterizes Pass amps. That is an amp designed first and foremost to be VERY easy to build. "Professionally" building an amp designed to be put together by a 12 year old doesn't strike me as a monumental achievement. It doesn't sound like you know much about Pass amps. Go try a SIT, a J2, or maybe and F4. That F4 is designed for line level stages like you're working with to enable them to drive an actual speaker load. 

It's not really a thing designed to add second order harmonic. It's a pot that balances the VAS. When the VAS is out of balance one way or the other it produces negative or positive phase second harmonic distortion. P3 in the F5 does the exact same thing, except with the F5 you're putting DC on the outputs when you turn it so you need to adjust it along with P1 and P2. 

That kind of adjustment makes a big difference. After having experimented with it quite a bit, I think Pass is dead right on his theories about distortion. If you want deep, enveloping, layered imaging, you want some negative phase 2nd order distortion.