I would imagine anyone spending big bucks on a DAC would of auditioned that unit in their own system and heard the sonic improvements themselves. I know my system pretty good, I've spent a lot of time tweaking it and finding where the weaknesses are. You would probably wouldn't be able to appreciate a high end DAC if your source was not up to par, so your transport or digital feeding the DAC would need to there, and of course the recorded material.
My digital setup never could approach my analog setup, no matter what I did. Never did I hear the quality of timbre, decay and naturalness of the struck piano key, as I head with my vinyl rig. Vinyl can be a pain in the butt to get right, but once it's setup right, with great material, high quality cartridge and amplification, you can be rewarded with sound that brings you emotionally involved with the music, almost an intoxicating effect. Now, if I found a DAC that could do that, like my analog setup, I would buy that DAC. Since I've listened to great vinyl, I got spoiled, and just could not sit and listen to digital that just didn't sound natural. I could listen to it, but it just didn't bring the emotional involvement that analog brought me.
I don't really want to buy an expensive DAC, but it's probably going to take a $2000 plus DAC to get the level of refinement that will produce that naturalness I've come to expect from my analog. I'm hoping the Audio-GD ref 7.1 will do that for me, that's the one I have my eye on and it's at the upper end of what I can afford, so if that don't do it for me, I doubt I would continue to dump coin into digital.