Well I just got my D1 today, and HOLY CRAP this thing is so crystal clear it's ridiculous. At first it sounded like I had lost a lot of bass punch, but then I realized that it was just better separation of the bass from the mids and highs giving an illusion of less bass. All the audio is completely pure out of a totally empty background. The DAC in the D1 is just incredible. The headphone amp, I'll have to do a lot more listening to before I make any judgments on, on first impression, though I'd say that the headphone amp is very close in sound quality to my m902, but the DAC is so much better that it sounds like it's in a completely different class. The highest impedance phones I have are my HD650's and at 300 ohms it seems to drive them quite well. I will say this though, the Grado's really sound great with this Amp/DAC and is slowly tempting me to sell the HD650's and get some RS1's.