Comparing E70 to a run-of-the-mill mp3 player (with the same headphones and same mp3 file), I find the sound quality of E70 a bit tinny. Not annoyingly so, but noticeably. Do you experience the same?
Could this be something a different mp3 program might cure? I see there are a number of alternatives for S60v3 - any recommendations?
Have you tried to fiddle with the equalizer in the built-in player? You might be able to get something of out it. Otherwise, use the trial versions of the third party MP3 players and see how they perform (i don't think that there are so many of them for S60 3rd edition anyway. In fact, there might be only one realeased yet plus another one that plays ogg files).
The R&B equalizer setting is better adds a little base (and you can edit it to increase it even more) but its still not quite as good IMO as a dedicated MP3 player or one of musicphones like the N91 or W810. For some reason the Hip-Hop preset has base but sounds flat. Not a musician so no idea why.