Low heat alternative to FIRSTWATT J2 ?

OK, I see you are making the distinction between Pass Labs and Nelson Pass's designs which would include First Watt. No problem. The F. W. are definitely a mixed bag of circuit ideas by him.
charles

It was mentioned above that all Pass/F.W. amplifiers use NFB.   The F2, F4, M2  and S.I.T. do not utilize NFB.
Charles 

Nelson Pass designed a 40 watt push pull version of the S.I.T. using the Sony VFET for the D.I.Y. community, it is pure class A. I used this amplifier in my system for 3 weeks recently. It gets very warm but not hot. I don’t see how the First Watt J2 (lower power, 25 watt @ 8 ohms) could result in a significant heat issue unless the room is unusually small and closed in.
Charles

Bojack I'm inclined to agree with you. I'd keep the First Watt compared to the other alternatives suggested. Not so sure they will sound better than the F.W. J2.