With respect to EQ, I have never found EQ to improve SQ. It can make a headphone or speaker with very poor frequency response listenable, but although said headphone or speaker, once EQ is applied, has a smoother frequency response, it will lose something with respect to it's realism. At the end of the chain, headphones and speakers are probably the components that add the most "flavour" to the listening experience. This is not really avoidable at reasonable budgets. I have found it best to pick your flavour and enjoy. I strive for minimalism in my setups. The less wire and components between the source and my ears the better. An equalizer is like adding the contents of the spice rack to the dish made by a master chef. Smooth FR is not as important to me than the feeling of being there with the musicians in the venue. EQ has always reduced that feeling of realism. Of course, everyone is different, so YMMV.