Andolink: Anda is correct in that I have the Ref 5.32 standalone DAC. As I mentioned in my last post, I really like this unit and think it sounds better than my old (second hand) Mark Levinson 360S DAC which was very highly regarded around 15 years ago. Regarding the sound of the NFB-6 amp, the only other amp I can compare to is one that a friend loaned me over Christmas along with his HE-500 headphones: it was a Little Dot Mk IV SE tube amp which I drove through my Ref 5.32 and this combination sounded really good. I did not get my NFB-6 until a few weeks after I returned the Little Dot amp so I did not have a chance to compare the 2 amps directly. But I thought the Little Dot was a nice, warm sounding amp, very musical and a nice match with the HE-500 headphones. And of course the tubes are really sexy! But now running the NFB-6 through the same Ref 5.32 and HE-500 combination, I enjoy this combination at least as much as I did with the the Little Dot. From memory, I think the NFB-6 allows the HE-500 headphones to give the same yummy richness of sound but with the bass more firmly in control and probably a bit more powerful. But for me the big plus of the NFB-6 is that it has balanced outputs whereas the Little Dot did not, which provides a distinct improvement in sound. I would love to do more comparisons!
Lorspeaker: thank you for your comment. I looked at the website you included in your post and found it interesting. Unfortunately it looked to me like Audirvana is for Macs while I am running a PC. But from surfing through related websites, I am coming to the conclusion that you are absolutely correct that the software decoding the lossless music files does make a difference. The problem is that I have a good sized iTunes library--all lossless--and PCs do not appear to have the same addons as Macs that allow iTunes to be retained as the management system while still improving the software the output sound qualtiy. I did come across Foobar which I need to investigate further, so you have definitely given me some more homework to do.