Hi could you please verify the comment from my customer below?
I interprete Your answer as follows:
To get +/- 1Vpp we need 70 Ohm instead 50 ohm to GND on each leg of the transformer.
Then we have a voltage of 1.4V at the DAC output.
Is there no conflict with the output compliance Range which is in the data sheet 1.25V (smaller als 1.4V)?