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

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 ?

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.

Wow, I didn't think that an amp was so sensitive to ambient temperature and vibration/movement that it would affect bias (for a solid state amp yet)!  I don't like touching the insides of an s.s. amp to adjust the trim pots with meters while on.  Yuk! 

None of the Pass products (including the classic Nelson Pass stuff) are engaging IMHO....

... from sound perspective

... and from my bullying friend's perspective (he keep bragging and preaching about his Pass)

Don't get me wrong.   They are fine products by any standard.  But just don't engage me at any level.   Almost like Boulder.  I feel like I am listening to an top notch electronic lab instrument.