For my source components I am using a PC with iTunes with lossless files, connected via a standard (i.e. cheap) USB cable to an Audio-gd Reference 5.32 DAC, which is connected to the NFB-6 via an Audio-gd ACSS cable. Do you have any recommendations for upgrades in this path? I was thinking of using JRiver for if/when I get into HD Audio, so do you think it is better than iTunes for sound quality? I would not think that the library software would make a difference, but I suspect this is a naive viewpoint. And does the quality of the USB cable make a difference? I have always been sceptical whether digital cables make much of a difference and would welcome advice from people with more experience. I have some pretty good Nordost XLR cables and plan on comparing them to the ACSS cable for connecting the DAC to amp, but I read a review that says ACSS is superior to XLR which is what I would hope.
As for the Audio-gd Reference 5.32 DAC, it was the first thing I purchased (on the advice of a friend) and I must say I am impressed with it. I have compared it via the optical inputs to my old-but-good-in-its-day Mark Levinson 360S DAC and the Audio-gd DAC is distinctly better: more body and 'rightness' in my opinion. Also it is an excellent match with the NFB-6.
As for the HE-500 headphones, my burn-in is complete and I am very impressed with the way they mate with the NFB-6. I read a review someplace that talked about the notes having a 'rounded' musicality and I totally agree. The combination is seductively musical, with pounding bass when called for up to shimmering highs. Having said that, from the brief listen I had with the NFB-6 driving HE-6 headphones, that combination had an attack and transperancy that I remember as being entrancing. Luckily, I will not be able to do more listening of this combination for another month or two, which means I can remain happy with my currenct purchases for a littler longer!