I just dug out my NW-HD5 after not listening to it for couple of years.
Wow, seriously good-sounding player. No idea how Sony achieved it. It can't play lossless (about 350kbps is the max). With no external amp it has a seriously impressive ability to power my headphones. It has a nice sound signature to it. It's quite warm but with a kind of dry clarity too, bass is punchy, instruments are separated nicely but work together beatifully. It just seems a very 'musical' player, especially compared to my s:flo2 (which is very powerful, but lacks that nice sound signature).
I might have to find a version of Sonic Stage somewhere so I can make this my main player. It must be almost 10 years old.