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

and the First Watt, X, and XA series all sound different...

jetter, I am almost certain that Pass would not be good enough for me, definitely not when high - for me - cost is involved. I would have to wait longer and go higher. Pass seems to be a solid choice, that's all.
As for the Ypsilon experience, there was something terribly wrong either in that system or with the listeners or both. Some do say that Ypsilon may sound a little bright and forward, but it depends on the rest of the components and preferred sound. Stage III cables are often used with Ypsilon.

Hi inna, I completely understand regarding cost.  I am thinking of what I believe is the least expensive amp, the XA25.

Yes, jetter, by all accounts for the price it is an excellent choice if you don't need more power and current. 
Besides various acoustic and vocal music, I listen to jazz rock, and with my current and I believe future speakers I would need more than what the Pass can deliver. That's in addition to what I said earlier. 

The Ypsilon preamp and phono preamp were driving Viva tube amps which were driving Avantgarde Trios and 3X Basshorns. Yuk! Switching out cabling from High Fidelity to GroverHuffman cabling made it listenable but still rather thin, bright and forward. Substituting Viva preamp and a custom designed tube pre-amp, wow, the sound mellowed and became enjoyable. We suspect that the phono preamp is also on the bright and forward side using a Kiseki on a Caliburn/Cobra setup. We also tried CDs. I know, Michael Fremer owns and believes the Ypsilon to be his favorite. Maybe in his system but not in the one I heard.