Read the owners manual of your DAC1 and it will explain the voltage level capabilities on both the variable and fixed (calibrated) settings. There are also tweakers inside the DAC1 that can be used to fine-tune the fixed settings.
With 0dbFS digital signal level, the DAC1 will output approximately 3VRMS in the variable mode with the volume pot CW, and about 2VRMS in the calibrated mode regardless of volume control position. There are some internal attenuators available also, but those are only on the XLR outputs.
Cheers,
Dave.