I really don't know how much EFB would do on one of these. Where that has a lot of benefit is in an AB amp where the current swings on the screen and cathode shift the voltages around. With a straight class A amp there isn't a whole lot of movement so any benefit is fairly minimal.
I have one of the lesser siblings, an AMP-197. The stock transformers were pretty poor and there was a nasty EQ curve that made it effectively useless as a stand-alone. Removing the EQ curve helped but spending the $40 on the cheapest aftermarket transformers that Amazon could provide to me using a gift card I had made a big difference. Circuit isn't quite the same but its not different enough in a way that truly matters. I could have easily done it as a DGSE1 but I left it slightly closer to the original design. I think mine has one less resistor but one more cap.
