It's mostly a matter of differences in the naming of the paramaters.

MAX5477
Address - Command - Data

I2CWRITE
Control - Address - Value

The I2C Control, is what the MAX calls Address.
The I2C Address, is what the MAX calls Command.
What you are calling Control_NVreg, is what the MAX expects for the Command.

Here's what it should look like without changing the variable names.
Code:
I2CWRITE PortA.6, PortA.2, Address, Control_NVreg,[Value]
                          %01010010    %00100001   %10000000
Also, your address indicates that the A0 pin on the MAX is tied HIGH, with A1 and A2 tied LOW.