I thought I should report on my feelings toward the D1-dual as time evolves.
I received a D1-dual a week ago or so, and had a few days to get to play with it.
The initial honey moon phase was excellent, I posted here about it: http://www.head-fi.org/t/439657/headamp-blue-hawaii-special-edition/6765#post_11278411
After some time though, going through my record collection with some less stellars than others, I started to notice some hardness to the sound when listening at moderately high volume levels with the SRM727/SR009 combo. Of course, I had already noticed the issue with the old dac but, suffice to say, the D1 is not the kind to polish a turd of a recording and make it all shiny... I saw myself just turning the volume down a notch in these instance, just to bring it back up the next tune around.
Now, as you may now, there is an FIR filter built into the dac that compensates for the high-frequency roll that is inevitable result of the "brickwall" reconstruction filter used with 44.1k material using a non-oversampling approach. Fortunately, the DAC designer offers the user a choice to engage / disengage the treble compensation filter (pretty much a 3dB boost at 20k with minimum added ringing).
While I was initially leaving it on with all my "audiophile" recordings, I am now finding myself just getting used to it being turned off as it makes the not so great recordings more palatable and does not actually feel like there's any drape being cast in front of the music. It is still surpremely dynamic and detailed while it never stops from sounding organic / music just flows with no dynamic restriction / no compression whatsoever.
Otherwise, the boomy bass I noticed from day one is still very much there, which makes me impatient for the upcoming amp upgrade. I have a feeling the stock SRM727 is indeed the weak link in the chain now and probably the culprit for the poor bass control and tendency to sound shrill if pushed to excessively high loudness levels...
As of now, I still have absolutely no regret with the absurdly crazy expense this D1-dual was. I tried to play back again the Yamamoto DAC, I could not stand it for me than 15 min.
I will post updates as my feelings evolving, be it frustrations or enjoyments. Probably that helps people make up their mind with their purchase decision....