What are the weak points of Pass amps and pre-amps ?

The weakness of Pass (I live in France) :- not unexpensive- of course there are better one at much higher price- hard to find used- " It will become clear that they lack realism in the individual focus of voices and instruments. When you listen to voices and instruments in real they are very small and direct. The Pass Labs preamp and power amp are not able to create the intimate focus as in real."I completely disagree after having played piano for over 35 years and along with a musician who has recorded as a soloist backed  the Concertgebouw the Beethoven Violin concerto. We could listen both to the rehearsal (hall empty) and to the concert (sold out). This is the point of other musicians
- User manual could be clearer- No Trade in available in France (they should had this point on their binding contracts with their distributors added) so upgrade is almost unaffordable.- IMHO, their amps are better than their pre
Pros :- keep on upgrading, trying new ideas and finding new solutions- can reach them and have you're questions answers quickly
- Pretty much on the melomane (music lover) side - faithfulness - rather than on the audiophile (sound lover) -more pleasure even if it implies distortion -.Some are melomane, some are audiophile, both points of view are equally respectable. I'm a melomane.
IMHO,  they are not designed to please everybody but to WYHIWIOTS (What You Hear Is What Is On The Support) .
So it's more a matter of love or dislike.
I love them.

A few say that Pass amps are better than preamps, not that preamps are no good. I heard the same about Rowland, Lamm and others. It appears that it is more difficult to make a great preamp than power amp. Who is going to make great preamps ? Let me guess - just a handful of tube guys, correct ?

127 degrees is not the normal operating temperature of my amp ( X-350.8 ). Just checked it with a heat gun after 4 hrs of play. It's 88 degrees.

88*F=31C which is probably too cool.  Nelson has posted elsewhere for older X series amps that 45-55C on the heat sinks is reasonable (along with what that subjectively feels like by hand in case you doubt the thermometer), and the manual for your 350.8 specs a temp of 53C (127F), so Pass recommendations seem historically consistent. Your amp could probably stand to have the bias increased a tad. At least on my old X150, the trimmer pots are so fricken sensitive that lifting the amp, carrying it across the room and gently setting it down will mess up the bias and offsets, so I readjust after I've moved the amp to where I want it. I shoot for 48C in winter time, so given the ambient temp changes in my man cave it will run about 50C in summer.