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

Alright, I think I get the picture.
bsimpson, I especially thank you. You confirmed my impression that was formed after reading all the posts and a few other threads and reviews.
Sound, whatever else it should be, must be engaging. Just like people, I could add.
So, practically speaking, it appears that I have no need for Pass.
From what I gather, brands like Gryphon and Ypsilon are not just better, not in another league, but in another universe. And that is worth paying for.

Hi inna, I have been considering purchasing a pass amp, so I have been following this thread. You inquired regarding the weak points of pass amps, and just guessing you received about 99 responses praising their sound, and two or three not positive responses. I thought the responses were overwhelming favorable, do you mind mentioning what lead you to think otherwise? Thanks

I have extensive listening to a high end Ypsilon preamp a new friend's home.  That and High Fidelity cables had me run from his listening room the first time.  After replacing the horrible cables, the preamp was the next culprit of an $850,000 system in producing bad sound.  It was replaced by a VIva pre-amp.  I doubt Pass pre-amps could sound as bad as an Ypsilon.

In my opinion, talking about amplifiers without mentioning the rest of the system, e.g., preamp, speakers, etc., is pointless. Most of the “engaging “ aspects of the sound quality comes from the amplifier pairing with the speakers., and in the right room. I’ve heard several moderately priced “systems” that were a lot more  engaging than systems costing multiple times more. 

I had a 350.8 so I'll address the heat issue. I found it surprisingly warm to the touch. But it did not heat the room.
I would have loved to have kept it but it was just too large for my small apartment.
As it is so small I am very sensitive to heat and stuffiness issues.
The temperature of the Pass in no way affected the atmosphere in my room. Others may have a different experience but this was mine.
Had it not taken up so much real estate(you really don't know do you unless you have it in your personal space)I would not have parted with it.