Trying to EQ low quality headphones, say some cheap ones from ebay, is like trying to make your pebble shine by polishing it. In my opinion, for the most part, frequency response is basically almost everything. Except for soundstage and imaging. Frequency response does have a play in soundstage and imaging, but there are other factors, like with over ears, the space between the driver and your ears, your pinna, the shape of your ear canal.