Fist Watt F6 vs Pass Labs XA 25

I’m thinking about an upgrade regarding my power amp which is a First Watt F6 dual mono (source: LAB 12 Dac 1 Reference, "speakers": Abyss 1266 PHI TC, preamp: Dave Slagle Autoformer).

I can’t say I wouldn’t be satisfied with this configuration but I’d like to try something even more engaging.

For the moment I’m intrigued by the XA 25 but never had the chance to give it a try in my system. 

Most of the reviews just compare the F7 to the XA 25 but I would be happy to hear experiences from users who had F6 and XA 25 side by side.

Is it worth an upgrade and which exact differences could I expect sonically?