Hey, it is really a fact that RE0 beats ER-4P quite easily, as ER-4P is a compromised solution for un-amped low-powered portable player. So I will not compare them at all, but not true in case of ER-4S. The RE0 and ER-4S both give same details but with different passion, where as RE0 presents the details with smooth edge like velvet or like feather touch but ER-4S presents the details with sharpness and loudness, one will feel the sound textures are more contrasting with ER-4S, with such sharp edge some people might find it little hurt with their sensitive ear. But many people would find the ER-4S more touchy and feel harder presence and they would prefer that hurt enjoyable. And due to this reason when you are listening to mp3 with lower bit rate, it will sound worse with ER-4S than RE0 as ER-4S will reveal the flaws more harshly than RE0. So if your primary source files are mp3 with lower bit rate than stay away from both of them especially keep yourself more distance from ER-4S. The RE0 will somewhat little cover up the flaws with its neutrality but the ER-4S will not. Now it is choice personal preferences. But I myself enjoy both of them differently but equally. I would suggest please try hard to afford at least an portable amp (not Fiio but others in between $70 to $150) to realize these two maestro, I can bet you never regret for the time you spending with these two.
Edited by srisaikat - 7/6/10 at 9:13pm