Both. Few started to say this and it became contagious. That's about it.
Did he matched the ADI-2 to either 2V (8.5dBu) or 3V (11.5dBu) to compare with the Qutest? I don't think so.
Of course, the louder will have the biggest soundstage...
Those dBu values are incorrect, unfortunately, making level matching the RME to other DACs actually a fair bit more difficult. 2 V RMS is 8.239 dBu while 3 V RMS is 11.761 dBu. Thus, if one only uses the volume control and output level settings on the RME and other DACs, there is at least a 0.239 dB difference in level which is probably too low to be audible as such but is most likely not without perceptual effect.
For a level matched comparison that allows for judging the handling of intersample overs, both the RME and the other DAC should be set up such that either one receives an unattenuated signal while the signal going to the other is reduced in level so as to match the output level of the two. To match the level between the configurations, the gains of the amplifiers should be raised or lowered accordingly. For example, in comparing the RME to a DAC with 2 V output level, the signal going to the RME set to -4.5 volume should be attenuated by 0.261 dB if it is sent unattenuated to the other DAC and if the signal is sent unattenuated to the RME set to -5 volume, the signal going to the other DAC should be attenuated by 0.239 dB. Further, if the signal is sent unattenuated to the RME, the gain of the amplifiers should be raised by 0.239 dB or if the signal is sent unattenuated to the other DAC, the gain should be lowered by 0.239 dB.