My point about blind tests is that I doubt whether anyone is going to go to the trouble of blind testing the various configurations - to do that properly is a remarkably complex exercise and unless properly done there's little chance of being able to draw a valid conclusion.
So all I can do is to consider the measurements. I can see no evidence that the R-44's frequency response would noticeably colour the sound of the incoming audio. "Transparency, warmth, depth, clarity, soundstage" are all subjective terms with no associated measurement criteria - well, ok, transparency could be deemed accuracy (what goes in is what comes out, and the R-44 appears to provide that) - warmth is usually applied to a frequency response that favours lower frequencies compared to higher frequencies, and again, I see nothing in the R-44 response which would provide that. Clarity - well, perhaps that's upper middle frequency emphasis. Soundstage - crosstalk, leakage from one channel to another would limit that. Otherwise thre should be no difference in "soundstage" from one device to another. It would have to be a pretty poorly designed preamp that didn't keep left and right adequately apart.
Generally if a preamp has a particular sound, I'd avoid it like the plague. It should be a piece of wire with gain. These days we are still stuck with the imperfections of loudspeakers and microphones but the rest of the signal chain should, if correctly designed, impart no significant character to the sound passing through it.
I have in mind a possible test of R-44 vs piece of wire...
