I personally do not like the whole ides and I have addressed it in here:
I am not nether equipment or electronics engineer but from what I see they also are very clueless in this subject. My feeling is that since it is imposable to make absolutely transparent buffer on tubes then any output tube is in a way a marking devise. In addition we truly can’t assess the topology itself as in D/A for instance they are very much merged with DAC topology, filter topology and so on. So, how one would distinct let say the imaging problems that come from tube vs. SS output stage from imaging problems that come from post-conversion filter? In way we look at the performance of a complete unit and this is all the we, end users, can do. with all things being equal I personaly try to avoid any digital with tubes in output stage.
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche