I'm here because I'm in the middle acquiring one from the usaudiomart. Online subjective reviews had been favorable against my XDA-2. However, I'm disappointed to learn the opamps on the DC-1 are not socketed like the XDA-2. The boutique TI opamps (forget the model) I have gone back and forth with stock on I *think* I prefer. My XDA-2 was re-capped out of the gate for reliability and (some will disagree ... too bad) sonics in the output section.
This whole ramble on the virtue of measurements and discarding your ears is bunk. Hearing happens in the mind and its apt to fool itself. Yes, so measurements serve as a good reality check. IMHO you need to use both with equal training. I'm not a measurement guy, but I know what I like when I hear it. One thing I've learned along the way is that good audio doesn't necessarily equate to expenditure of funds - but mostly takes determination, trial, willingness to learn and a healthy distrust of your own bias.
I also saw in this thread a casual stone thrown in the name of psychoacoustics regarding long term tests. I assume this is because audio memory is poor and mostly useless. I actually found both long and short tests to be helpful depending on mood, mindset, focus. I can live for a week or more with a device and swap it, the difference can be shocking at first, but then it can fade. I found this to be true between tube make and model. Other things like this Aegir vs Vidar or preamp/no preamp test I'm doing is immediate and obvious. I've done A/B tests and heard no difference, but the same test over time to acclimate allows your mind to learn, to lock in on cues that allow you to recognize a differences. Discounting results because you're flipping between two devices instantly and hearing no difference does not mean that there's no difference, only that you can't hear it in the short time you gave yourself. This is especially true of untrained listeners who only know how to gyrate to the distorted squawks and squeaks of their tin can ghetto blaster crap. *shiver*
Whatever method you use, so long as it moves you to a better equipment selection, I think your going in the right direction. But how do you tell, especially between small increments? I don't know.
Regardless. I'll see if I like the DC-1 over the XDA-2. No other way to find out than to try it.