Pass Labs XA and XA.5

Has anyone any ideas on the difference (sonically) between the XA and XA.5 amps from Pass? I have the XA 60. I have had almost all of the Alephs, an x350 and an x350.5. The 350.5 was a big improvement on the x350 but I wonder about the XA.5. It is three gain stages instead of the two in the XA. A lot more power into lower impedences obviously. I am wondering if the first 60 watts of the XA.5 sounds better than the first 60 out of the XA. J fets are great but that is a lot of $ for four transistors. I assume the XA.5 is a step closer to the x.5 series. Nelson has come full circle and hit all the power requirements for each market. I know the XA sounds better than the Aleph 2's I had...which is saying a lot. But I think the Aleph 2 sounded a lot better than the OS which had three stages. Thoughts? and thanks