Thanks for the feedback. As I continue to talk to people and read it is becoming clear that the .5 model change is important. The CLS likes a lot of power and the impedance can dip down to 2 ohms, so the amp has to be stable. I understand that the original XA series had issues with handling low impedance speakers, but this was corrected in the .5 series. The pure class A power of the XA is supposed to be phenomenal sounding, but the class A watts are more expensive. On the other hand, I have read that you don't need as many class A watts to drive the same speaker. I have seen comments that the X350.5 and the XA100.5 are the "sweet spots" in the Pass Labs model line up in terms of power that can handle most speakers and bang for the buck. If the choice is between the X350.5 (MSRP $11K) and the XA100.5 (MSRP $16K), then what would you say?