Hi,
ER's doc mentions that the er6i with shaped bass are not as accurate as the er6. Is there any (negative?) impact on the sound fidelity (for I generally listen to classical music and look only for accuracy)? And are the er6 also fit to be directly driven by an mp3 player?

OK, no help yet. What I have to offer is not much help, but I do have the higher priced Etymotics and have had them for manyyears. They are stellar. Their bass will cause bowel movements. I would guess the less expensive in-ear earphones are pretty good, too. Get a deal where you can return them, yes??

The ER-6i has an altered frequency response to correct for ipod output and perhaps other portable players. The ER-6 will benefit from an amp, particularly one with a low output and noise floor (since it is very sensitive) but some players may be able to do a good job with it. I had an ER6 and didn't find it great for classical music. The ER4 is better, still not great, but the best at a reasonable price if you need sound isolation.

Thx.