Heyo dmiles32
If your source is of sufficient quality, then a AMP/DAC combo could improve the quality of your headphones. The placebo effect will probably make you think it's better, however in reality it's probably just louder.
For high-end headphones a AMP/DAC will make a world of difference since they have the fidelity to bring everything up. Lower quality headphones won't benefit as much since they won't be able to really bring up the details.
Now then... As for what goes for EQ's. It might make them better. Again, it's up to the individual to decide what sounds good. Personally I really like my sound signature to be flat, hence why I got the HD800's and I wouldn't change a thing about them. If you feel like there's a lack in the...