(Old thread, I know.)
My old Cowon player has given me some problems of late, so I was considering using the N9 as my music player No contest against the Cowon--N9 sounds so dull. To my surprise my old N900 is a much closer race (though still loses). I could--and probably will--settle on theN900. The N9 sounds clean but really lifeless--kind of 2D. I am surprised so many people think the N9 sounds better.
I have found that in terms of the audio quality coming out of the device, iPhones sound a lot clearer. I tend to find the audio output quite muddy and weak on my N9 compared to that of my friends ipod<SNIP>
I used/use a pair of Sennheiser CX310's.