He has measured the Lynx Hilo and Benchmark DAC3 at 24 and 34 dBu. However, that was more than a year ago.
Anyways, as the RME can also be used as a preamplifier, I think measuring at its full output level is relevant.
Further, as I said before, I think noise will dominate any measurement with input level below -3 dB FS. With the volume set to -4.5 dB, the highest input level will be lower than that and will just show the SNR increasing with increasing level while with the volume set to 0.0 dB, the highest input level will be higher and the amount of distortion at higher levels can be evaluated while retaining most of the information the measurement at -4.5 dB would have provided.
Thus, to refine my suggestion, I think that
@amirm should do the dashboard for both the common 2V / 4V and 13 dBu/19 dBu while doing the other measurements with volume at 0.0 dB at 13 dBu/19 dBu.