Pass 's xa series is this his best so far?

Pedrillo, there are 2 Pass XA series, the original XA and the newer XA.5. . . . Which one are you referring to? G.

The xa.5 series.

Pedrillo, the XA.5 was never meant to be a revolutionary departure from the original XA series. As far as I know, the primary design goal was to extend compatibility and high 'torque' for lower impedance speakers that were not as adequately driven by the original XA series. Thus, Pass broaden the market appeal/applicability of the XA series. G.

Padrillo,
You can read my review of the XA100.5 on Audiogon in which I compare it to the many other Pass amps I have owned for a subjective impressions of the differences. I think Guidocorona is correct in describing the increase in power for lower impedances as the "primary goal" of the XA.5 but there are some other changes as well mentioned on the Pass website. You could also try contacting Pass.