I came across this situation where I have a headphone that requires eq and I have music players or DAPs that does not have eq. I know music files are just zeros and ones. But I'm thinking that you can add eq to them. And I don't know of an app that can do this. Has anyone done this?

Anyone know the details on the internals of this? https://www.ebay.com/itm/Polk-Audio-Melee-Headphone-Xbox360Xbox-One-Black-B/183660364114?hash=item2ac302c152:g:UR8AAOSw7MNcULl~ The Polk amp has only optical input and trrs plug output with some controls and mic plug for a gaming system. But I...