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

Since you are interested in the difference between XA and X, call Kent English at Pass.  5308785350

I have the XP-12 which can turn on the XA60.8. The Ayre preamp couldn't. I needed that functionality.

Wayne, the designer of the preamps told me that the XP-10 cannot turn on the XA60.8. 

The combo is good to my untrained ears.

 If you are worried about the price of Pass amps and happen to have efficient speakers, try the First Watt line. Wonderful amps that won't break your bank.

I have not heard all of Pass Labs amps, but from recollection of a few I did owned it’s good but not great.
I had the X350, X350.5, XA100.5, XA160.5, XA160.8, compares to MSB M202, M203, Lamm M2.2 and ARC REF250 and even Bryston 28B3, one would wonders what the hypes was all about.
As you can see, I did fall for the hypes with owning 5 different Pass models.
Not bashing on Pass, I’m sure the XS is a must for class A enthusiast, including myself.

@medwardo - I have the X250.5 driving my sophia 3s and have the itch to move to an all class A. Even though the X250.5 offers the first 25W in class A. I spoke with Pass and they didnt think highly of a move from the 250.5 to the XA30/60.5. They did mention that a move to XA100.5 will be very rewarding and worth the move. Is your XA25 able to drive the Sophias well? They are known to dip well below 2 ohms at low frequencies.

pistha, while you were talking with Pass Labs did you ask them their opinion regarding the XA25 driving your Sophias? I ask because I believe my speakers also dip rather low although I only know their nominal impedence.