So far you have seemed to miss the point .. I would like to see a scientific measurement that compares one with another using music (so ears and arbitrary tones do not get involved) .. seemes a bit closed shop to assume we have all the measurements we need as just a bunch of tones.
That is only ever requested by people who don't understand how the waveform of real music is made up of a set of sinewaves, AND / OR the mechanisms by which distortion/noise are created in audio equipment. You don't need to test a device with real music in order to understand how real music is changed by that device.
I keep having to say this - but there is nothing mysterious about audio electronics. It is pretty much the simplest application of electronics - so much so that it was the first application of electronics over 150 years ago. We know, by now, how to do it, how it works, and how to test it.
Also if a difference is obvious at pretty much any level why would you need level matching? So simpler test to illustrate.. my TV has line out from its DAC .. it sounds pretty *hit and is easy picked out at any level agains the rme... They don't need to be level matched to assess that.
A difference can *seem* obvious if your sources are NOT level matched. IE you hear the different level of one and that:
a - allows you to identify which you are listening to, so not blinded .. and..
b - might make one sound better than the other.
If you don't level match (as well as the other necessary controls) you haven't blind tested.