OK, I talked to a rep at Bogner and this is the jist of what he said.
Rev1 = very high plate voltages and sharp taper on the gain.
Rev2 = very high plate voltages and smoothed taper on the gain.
Rev Blue = lower plate voltages, smoothed taper on the gain, voiced slightly differently, more PCB contruction, loop level control and external bias test points.
I'm assuming the higher plate voltages are probably the reason why they specify JJ/Tesla EL34's in the amp.
As a side note:
I did ask if it were possible to have a XTC head built with the Red channel built the same as the Uberschall high gain channel and he said it's not possible as there many components that make the Uberschall different/special. He did say that they get asked that a lot, so who nows, maybe one day.