The analogue circuit board used in the ISA428 MkII is exactly the same board used in the original.
Here is a summary of the changes made to the ISA428 MkII:
• Analogue ‘moving coil’ peak meters have been removed.
The LED meters remain on the ISA428 MkII and sit in the signal chain before the A-D converters.
• The Soft Limiter feature has been removed.
• The bit depth selection button has been removed from the front panel.
There are now more superior methods to make changes the bit depth from within a DAW.
• The linear power supply has been replaced with a switched-mode power supply.
The new power supply automatically switches between input voltages. It can be plugged into most mains power supplies around the world without changing a voltage selector or a fuse.