BAT REX amps

I would appreciate input from people who have upgraded to the BAT REX amp (either Mk. I or Mk. II) from the VK-75SE. I would also appreciate any comments Victor ("Chipmunk") would like to make about important technical differences between the two amps, for example, do they use the same output transformers and have the same energy storage? Is the basic difference just better quality parts or are there also differences to the circuit?

Thanks in advance.