As far as I can tell the only thing the Sony has over the Iriver2 is the G-Protection - if it's anything like my Sony D-915 then it's definitely better than the Iriver2 model.
Other than that, I strongly suspect the Iriver2 has got it beat - better display, louder, near remote control on the headphone cable, sophisticated EQ settings (normally I don't use them with with MP3 the odd bit of boost can work well!), Winamp playlist support, better programming, etc, etc.
I think the Iriver2 is an excellent machine. Whilst not up to the sound quality generated by the Sony D-915 and Panasonic 570 discman players, it's really very close. It does suffer with some line noise but then again so does my Airhead amp. I tend to not notice either once the music starts playing.