I'm resurrecting a dead thread for the benefit of future generations. I assume you've already purchased something. For those who haven't...
The NuForce Icon HD sounds fantastic. It is really, really good for the price. It's great with the HD650s and most AKG cans as well. Something you need to know, though, is that the increased brightness that's thrown into CDs comes through, so some phones don't pair as well with it. The HD650's do particularly well with it because of their darker nature. So do AKG K171's; they actually have bass now and it's wonderful.
Something I've found out with DAC / HP Amp combos though is that volume is controlled in three different places: the media player, the computer's master volume control, the amp itself. Because the Icon HD has such power, I've put my media player (WMP) up to max, turned the system, volume down to 10% (just as a test to get started), and turned the Icon HD on to 9 o'clock (when vertically standing the unit). From there I dialed the system volume up until I was comfortable with the sound but it was still quiet. The system volume, in my case, is at 70% and I can turn the Icon up to about 11 o'clock and it gets tremendously beautiful. At that point, the amount of attenuation through the pot is such that there's no more noise and everything is in the sweet spot... sonically magical.
Can you tell that I was supremely impressed with this thing? I knew the Icon HD would sound better than without, but I didn't expect it to sound as good as it did. For the money, I can't think of anything that comes close in performance.
If you have some cans that are easy to drive, then you need to bring the volume down on your computer or you'll be so low on the volume know with the Icon HD that you won't have balanced output between the channels and there will be some hiss. Some people try to avoid dropping the volume on the computer, but whatever it takes to get the Icon HD up to the sweet spot is more worth it than dealing with the issues the arise from a low volume pot.
