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

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.

@inna, I don't think the X series or the XA series is "better" than the other absent the type of speaker you're trying to drive.  FYI I was all ready to purchase the XA series monos and Kent at Pass told me that the X series was better suited to my speakers, Thiel 2.4s.  The ONLY possible fault I can come up with is that there ARE solid state amps that provide bass that is tuned tighter than the Pass products although I think the X series is a little better than the XA series in that regard.  Its all speaker dependent.

pwhinson, when you previously wrote that Pass recommended the X series over the XA series I wondered if they mentioned to you why they made that recommendation?  I am sorry to say that I have never heard a Pass, but it would seem that either series has high wattage amps that will drive most speakers, and that which you purchase is a matter of whether or not you prefer a class A sound and a matter of costs? 

Hi kosst, I think that opens up a whole can of worms of whether a low or high efficiency speaker inherently sounds the best? One would think that if all high efficiency speakers sound better than their low efficiency counterparts there would be no need for higher powered amps as there would be no speakers needing that power.

Now going off thread, I guess the question is what are the advantageous and disadvantageous of low and high efficiency speakers?