The ADI-2 Pro has 24 dB digital headroom because it uses EQ. An overload of the output is clearly shown on the level meters (other than with most DACs out there), so reducing the 'Volume' in such a case will be done by the user automatically and intuitively, so that there is no overload at all.
The DACs used in RME units plus their analog output stage typically have 2.5 dB headroom with low out-of-band distortion, so even if you set volume to zero with EQ disabled and apply such intersample peaks what you saw in the Benchmark docs is no issue here.
The only stage in the Pro where such intersample peaks can cause increased distortion is the Sample Rate Converter. But that is easily avoided by not exceeding -3 dBFS peak level into the ADI's digital inputs when using the SRC. And DIGICheck will tell you if that is necessary or not, as its 4 Bar Level Meter has an Option 'Oversampling' which activates the display of levels higher than 0 dBFS, directly read from the AES, SPDIF and even analog input.