The differences are relatively small in terms of circuit. Here are some of the minor technical changes:
* Small increase in driver plate current, which makes it practical to use an unbypassed resistor for quieter biasing.
* Excess filament voltage, reduced with resistors, allows more adjustment for power line variations.
* New power transformer (shared with Seductor), has multi-voltage primary windings.
* Point-to-point power supply replaces circuit board.
* Replace some obsolete components with modern parts.
The main focus (in my mind anyhow) was to make it upgradeable to Paramount-level sound quality. Not all the upgrades have been announced yet.