Is there actually a difference?

When I asked about the viability of adapting the F5 to power JFETs he pointed me to an example he'd built using the Sony devices

Sure- but that's not the same as saying they are the same. Google is your friend.

SITs are not in production- power JFETs are.

Interesting discussion, which I am joining late. I recently (about a year ago) purchased a pair of Magnepan 1.7i’s These speakers are not particularly easy to drive, so I knew I would need a few watts. Having blown my budget on the speakers, I went searching for a bargain amp.

I found a Parasound H2200 (300+ w/pc rms) on ebay for about $400. This seemed to have plenty of power, but the speakers did not sound like they did in the dealer’s listening room. The dealer was AR dealer and he auditioned the speakers with some pretty high end tube equipment.

I tried a couple of different SS pre-amps, but was not satisfied. Finally, I decided to try a tube pre-amp. After doing a bit (a large bit, actually) of research I decided to try the Transcend 6SN7 preamp (can you guess what kind of tubes it uses?). Wow!! Now I can’t say if they sound as good as they did powered by all that Class A tube equipment, but this seems to be a good pairing.

The Aric Audio gear really opened up the sound of the Magnepans. Maybe someday I will try some Class A Tube power amplification, but I don’t know how to compare the numbers (How does 68w Class A amplification compare to 300w Class A/B under a difficult load?)
Anyway I am satisfied for now. And my next $3000 expenditure will be for a nice (fairly) high end double boiler Cappuccino machine. Priorities. :)

1 of my local dealers manages to keep a straight face when suggesting output is the only difference between amps is output! Component matching is important and makes a real audible difference and properly matching an amp to speakers will have audible results.