Frogman,
Another thoughtful post as usual.For someone who does`nt have a 300b based system you sure described their attributes very well.To tell the truth you can play pretty much any genre of music'with the proper speaker match'.All amplifiers regardless of topology or power will have some degree of inherent limitations(I know of no exceptions). It just depends of individual listening priorities and what compromise you`ll except in exchange. Certainly jazz fusion and big band can sound wonderful,I play lots of Duke Ellington and Gil Evans big band.Every type of amplifier has it`s area of strength.I could be just as happy with an 845 amp based on whatI`ve heard of them.
Within 300b or any amp type there`s always a hierarchy,just pick a good quality one and you`ll be very pleased.My 8 watt 300b SET replaced an excellent push pull 100 watt amp 3 1/2 years ago and there`s no going back. A bit less bass weight and presence but other than that I find the SET just a better communicator of the music, of course YMMV.Frogman, I suspect you`d really like a well set up 300b system.
Regards,,