I can't compare any First Wattt amp with a Pass amp, but, just yesterday, I borrowed a friend's J2 to try in my system. It is being used to drive 99 db/w speakers with a nominal 8 ohm impedance, so the match seems reasonable.
On a basic, operational level, the J2 is very insensitive (needs higher line level to drive it to a given volume level than most amps). While that should not be an issue in most systems, this may be an issue with passive linestages. Also, it does take a while after turn on to sound its best. It tends to sound a bit dynamically dull, harmonically thin, and lacking in bass until it warms up (the first 5-10 minutes is particularly bad, and it continues to improve over an hour period). The good news, for people with really sensitive speakers, it make absolutely no turn-on or turn-off noise.
I was quite impressed with the overall sound of this amp--it is very clear, fast and dynamic, with only a hint of the kind of artificial "edge" to the initial attack of a note that is common to solid state amps. It does not have the bleached, "dry" sound that also found with some amps (both solid state and tube based). Music from this amp sounds very lively and engaging (very much unlike solid state with a lot of negative feedback, which sounds lifeless and flat).
In comparison to the parallel single-ended triode tube amp I use in my system, the J2 has some shortcoming when it comes to soundstage--it does not develop a huge, enveloping soundstage, and does not quite present the notes as blooming into a large space--the sound is much more directly in front of the listener and contained within the boundaries of the speaker, and the overall ambient "space" seems smaller. The other shortcoming is that it does not present the same kind of "dense" harmonic structure that my tube amps deliver. I don't want to overemphasize the shortcomings because, while apparent in direct comparison, the overall presentation is very musically enjoyable. Also, this comparison is not "fair" because my system has been tuned to my current amps, and these amps are WAY more expensive than the J2s. I will have them for a few more days, and I am sure I will have a lot of fun with them.
