I heard the same D7 as Rasmushorn this weekend and A/B tested it against my HRT HeadStreamer. I thought I was going to replace the HeadStreamer and get a D7 instead, but I'm keeping the HRT. The D7 sounds great, no doubt about it, but the HRT just has better clarity and a more open and spacious sound. I A/B'ed them using my Westone 3 and a set of AKG K701. They were both great with the W3 but none of them had the oomph to drive the powerhungry beast that is the K701 to it's full potential.
I really do like the volume knob on the D7 and the fact that it has RCA out on the back, makes it way better for semi-permanent desktop duty.
Ahh, don't make me regret my choice of getting the D7! J/K... I'm actually pretty happy with the D7, though I should definitely go try the HeadStreamer out when they finally get stock in here! I'll say that the D7 can be warm-skewed and that leads to a lesser perception of clarity, but it's definitely the most resolving DAC/amp I've heard, surpassing the DACPort, to my ears. The line-out actually ups the clarity a notch with IEMs, but lacks the bass control for cans. It's a good thing I have an HD598 and not a K701! My cans are driven very well with the D7.